feat(jsr.json): change main export path

The main export path in jsr.json has been changed from "." to "./index".
This change is to improve the clarity of the export structure.

packages/unplugin-typia/jsr.json

@@ -2,7 +2,7 @@
 	"name": "@ryoppippi/unplugin-typia",
 	"version": "0.2.0",
 	"exports": {
-		".": "./src/index.ts",
+		"./index": "./src/index.ts",
 		"./api": "./src/api.ts",
 		"./vite": "./src/vite.ts",
 		"./webpack": "./src/webpack.ts",