feat: add Matija's Homepage realm to examples (gnolang#2916)

### Summary
This pull request adds a new realm example to the Gno `examples`
repository—Matija's Homepage. It showcases a personal homepage built on
the Gno chain where users can interact by voting with GNOT tokens to
change the page's color. The more tokens users send, the greater
influence they have on the color scheme, providing an interactive and
dynamic experience.

### Key Features
- **Profile Section**: Displays a personal profile with an image and
description.
- **Color Voting**: Users can vote for the page's color (red, green,
blue) by sending GNOT tokens. RGB values are adjusted based on the
amount sent.
- **Dynamic Updates**: The homepage dynamically updates the color based
on votes, showcasing real-time interaction on the Gno blockchain.
- **Links to GitHub and LinkedIn**: Includes buttons for GitHub and
LinkedIn, making it easy for users to connect.

### Tools & Technologies
- Utilizes Gno's native functions to handle voting and token transfers.
- Provides a simple, yet effective example of how personal realms can be
interactive and engaging on the Gno platform.

### Why this is valuable
This example highlights the possibilities of personal realms on Gno,
showing how users can create unique and interactive profiles. It’s a fun
and approachable entry point for anyone new to Gno development, while
also demonstrating the platform's flexibility and potential for creative
expression.

---------

Co-authored-by: Morgan <[email protected]>
Co-authored-by: Leon Hudak <[email protected]>

examples/gno.land/r/matijamarjanovic/home/config.gno

@@ -0,0 +1,64 @@
+package home
+
+import (
+	"errors"
+	"std"
+)
+
+var (
+	mainAddr   = std.Address("g1ej0qca5ptsw9kfr64ey8jvfy9eacga6mpj2z0y") // matija's main address
+	backupAddr std.Address                                               // backup address
+
+	errorInvalidAddr  = errors.New("config: invalid address")
+	errorUnauthorized = errors.New("config: unauthorized")
+)
+
+func Address() std.Address {
+	return mainAddr
+}
+
+func Backup() std.Address {
+	return backupAddr
+}
+
+func SetAddress(newAddress std.Address) error {
+	if !newAddress.IsValid() {
+		return errorInvalidAddr
+	}
+
+	if err := checkAuthorized(); err != nil {
+		return err
+	}
+
+	mainAddr = newAddress
+	return nil
+}
+
+func SetBackup(newAddress std.Address) error {
+	if !newAddress.IsValid() {
+		return errorInvalidAddr
+	}
+
+	if err := checkAuthorized(); err != nil {
+		return err
+	}
+
+	backupAddr = newAddress
+	return nil
+}
+
+func checkAuthorized() error {
+	caller := std.GetOrigCaller()
+	if caller != mainAddr && caller != backupAddr {
+		return errorUnauthorized
+	}
+
+	return nil
+}
+
+func AssertAuthorized() {
+	caller := std.GetOrigCaller()
+	if caller != mainAddr && caller != backupAddr {
+		panic(errorUnauthorized)
+	}
+}

examples/gno.land/r/matijamarjanovic/home/gno.mod

@@ -0,0 +1 @@
+module gno.land/r/matijamarjanovic/home

examples/gno.land/r/matijamarjanovic/home/home.gno

@@ -0,0 +1,238 @@
+package home
+
+import (
+	"std"
+	"strings"
+
+	"gno.land/p/demo/ufmt"
+	"gno.land/p/moul/md"
+	"gno.land/r/leon/hof"
+)
+
+var (
+	pfp        string // link to profile picture
+	pfpCaption string // profile picture caption
+	abtMe      string
+
+	modernVotes  int64
+	classicVotes int64
+	minimalVotes int64
+	currentTheme string
+
+	modernLink  string
+	classicLink string
+	minimalLink string
+)
+
+func init() {
+	pfp = "https://static.artzone.ai/media/38734/conversions/IPF9dR7ro7n05CmMLLrXIojycr1qdLFxgutaaanG-w768.webp"
+	pfpCaption = "My profile picture - Tarantula Nebula"
+	abtMe = `Motivated Computer Science student with strong
+                analytical and problem-solving skills. Proficient in
+                programming and version control, with a high level of
+                focus and attention to detail. Eager to apply academic
+                knowledge to real-world projects and contribute to
+                innovative technology solutions.
+                In addition to my academic pursuits,
+                I enjoy traveling and staying active through weightlifting.
+                I have a keen interest in electronic music and often explore various genres.
+                I believe in maintaining a balanced lifestyle that complements my professional development.`
+
+	modernVotes = 0
+	classicVotes = 0
+	minimalVotes = 0
+	currentTheme = "classic"
+	modernLink = "https://www.google.com"
+	classicLink = "https://www.google.com"
+	minimalLink = "https://www.google.com"
+	hof.Register()
+}
+
+func UpdatePFP(url, caption string) {
+	AssertAuthorized()
+	pfp = url
+	pfpCaption = caption
+}
+
+func UpdateAboutMe(col1 string) {
+	AssertAuthorized()
+	abtMe = col1
+}
+
+func maxOfThree(a, b, c int64) int64 {
+	max := a
+	if b > max {
+		max = b
+	}
+	if c > max {
+		max = c
+	}
+	return max
+}
+
+func VoteModern() {
+	ugnotAmount := std.GetOrigSend().AmountOf("ugnot")
+	votes := ugnotAmount
+	modernVotes += votes
+	updateCurrentTheme()
+}
+
+func VoteClassic() {
+	ugnotAmount := std.GetOrigSend().AmountOf("ugnot")
+	votes := ugnotAmount
+	classicVotes += votes
+	updateCurrentTheme()
+}
+
+func VoteMinimal() {
+	ugnotAmount := std.GetOrigSend().AmountOf("ugnot")
+	votes := ugnotAmount
+	minimalVotes += votes
+	updateCurrentTheme()
+}
+
+func updateCurrentTheme() {
+	maxVotes := maxOfThree(modernVotes, classicVotes, minimalVotes)
+
+	if maxVotes == modernVotes {
+		currentTheme = "modern"
+	} else if maxVotes == classicVotes {
+		currentTheme = "classic"
+	} else {
+		currentTheme = "minimal"
+	}
+}
+
+func CollectBalance() {
+	AssertAuthorized()
+
+	banker := std.GetBanker(std.BankerTypeRealmSend)
+	ownerAddr := Address()
+
+	banker.SendCoins(std.CurrentRealm().Addr(), ownerAddr, banker.GetCoins(std.CurrentRealm().Addr()))
+}
+
+func Render(path string) string {
+	var sb strings.Builder
+
+	// Theme-specific header styling
+	switch currentTheme {
+	case "modern":
+		// Modern theme - Clean and minimalist with emojis
+		sb.WriteString(md.H1("🚀 Matija's Space"))
+		sb.WriteString(md.Image(pfpCaption, pfp))
+		sb.WriteString("\n")
+		sb.WriteString(md.Italic(pfpCaption))
+		sb.WriteString("\n")
+		sb.WriteString(md.HorizontalRule())
+		sb.WriteString(abtMe)
+		sb.WriteString("\n")
+
+	case "minimal":
+		// Minimal theme - No emojis, minimal formatting
+		sb.WriteString(md.H1("Matija Marjanovic"))
+		sb.WriteString("\n")
+		sb.WriteString(abtMe)
+		sb.WriteString("\n")
+		sb.WriteString(md.Image(pfpCaption, pfp))
+		sb.WriteString("\n")
+		sb.WriteString(pfpCaption)
+		sb.WriteString("\n")
+
+	default: // classic
+		// Classic theme - Traditional blog style with decorative elements
+		sb.WriteString(md.H1("✨ Welcome to Matija's Homepage ✨"))
+		sb.WriteString("\n")
+		sb.WriteString(md.Image(pfpCaption, pfp))
+		sb.WriteString("\n")
+		sb.WriteString(pfpCaption)
+		sb.WriteString("\n")
+		sb.WriteString(md.HorizontalRule())
+		sb.WriteString(md.H2("About me"))
+		sb.WriteString("\n")
+		sb.WriteString(abtMe)
+		sb.WriteString("\n")
+	}
+
+	// Theme-specific voting section
+	switch currentTheme {
+	case "modern":
+		sb.WriteString(md.HorizontalRule())
+		sb.WriteString(md.H2("🎨 Theme Selector"))
+		sb.WriteString("Choose your preferred viewing experience:\n")
+		items := []string{
+			md.Link(ufmt.Sprintf("Modern Design (%d votes)", modernVotes), modernLink),
+			md.Link(ufmt.Sprintf("Classic Style (%d votes)", classicVotes), classicLink),
+			md.Link(ufmt.Sprintf("Minimal Look (%d votes)", minimalVotes), minimalLink),
+		}
+		sb.WriteString(md.BulletList(items))
+
+	case "minimal":
+		sb.WriteString("\n")
+		sb.WriteString(md.H3("Theme Selection"))
+		sb.WriteString(ufmt.Sprintf("Current theme: %s\n", currentTheme))
+		sb.WriteString(ufmt.Sprintf("Votes - Modern: %d | Classic: %d | Minimal: %d\n",
+			modernVotes, classicVotes, minimalVotes))
+		sb.WriteString(md.Link("Modern", modernLink))
+		sb.WriteString(" | ")
+		sb.WriteString(md.Link("Classic", classicLink))
+		sb.WriteString(" | ")
+		sb.WriteString(md.Link("Minimal", minimalLink))
+		sb.WriteString("\n")
+
+	default: // classic
+		sb.WriteString(md.HorizontalRule())
+		sb.WriteString(md.H2("✨ Theme Customization ✨"))
+		sb.WriteString(md.Bold("Choose Your Preferred Theme:"))
+		sb.WriteString("\n\n")
+		items := []string{
+			ufmt.Sprintf("Modern 🚀 (%d votes) - %s", modernVotes, md.Link("Vote", modernLink)),
+			ufmt.Sprintf("Classic ✨ (%d votes) - %s", classicVotes, md.Link("Vote", classicLink)),
+			ufmt.Sprintf("Minimal ⚡ (%d votes) - %s", minimalVotes, md.Link("Vote", minimalLink)),
+		}
+		sb.WriteString(md.BulletList(items))
+	}
+
+	// Theme-specific footer/links section
+	switch currentTheme {
+	case "modern":
+		sb.WriteString(md.HorizontalRule())
+		sb.WriteString(md.Link("GitHub", "https://github.com/matijamarjanovic"))
+		sb.WriteString(" | ")
+		sb.WriteString(md.Link("LinkedIn", "https://www.linkedin.com/in/matijamarjanovic"))
+		sb.WriteString("\n")
+
+	case "minimal":
+		sb.WriteString("\n")
+		sb.WriteString(md.Link("GitHub", "https://github.com/matijamarjanovic"))
+		sb.WriteString(" | ")
+		sb.WriteString(md.Link("LinkedIn", "https://www.linkedin.com/in/matijamarjanovic"))
+		sb.WriteString("\n")
+
+	default: // classic
+		sb.WriteString(md.HorizontalRule())
+		sb.WriteString(md.H3("✨ Connect With Me"))
+		items := []string{
+			md.Link("🌟 GitHub", "https://github.com/matijamarjanovic"),
+			md.Link("💼 LinkedIn", "https://www.linkedin.com/in/matijamarjanovic"),
+		}
+		sb.WriteString(md.BulletList(items))
+	}
+
+	return sb.String()
+}
+
+func UpdateModernLink(link string) {
+	AssertAuthorized()
+	modernLink = link
+}
+
+func UpdateClassicLink(link string) {
+	AssertAuthorized()
+	classicLink = link
+}
+
+func UpdateMinimalLink(link string) {
+	AssertAuthorized()
+	minimalLink = link
+}