Fix : Update meta title error handling

[sossost]

Closes #26642

What I did

The error message that appears when the story file title ends with '/' has been appropriately modified.

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

Tested in sandbox.

Run a sandbox for template, e.g. yarn task --task sandbox --start-from auto --template react-vite/default-ts
Open Storybook in your browser
Create a story file whose title ends with /.
Check if an appropriate error message such as is displayed. 'Invalid title Example/�Component/ ending in slash.'

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli/src/sandbox-templates.ts

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

🦋 Canary release

This PR does not have a canary release associated. You can request a canary release of this pull request by mentioning the @storybookjs/core team here.

core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=<PR_NUMBER>

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[ndelangen]

@JReinhold does this look OK to you?

[JReinhold]

The current error message highlights that this happens if slash is anywhere in the name, not just at the end. If that's still the case, then the proposed error message here is too misleading.

[sossost]

@JReinhold
Added error message branching.
Now, when the title ends with '/', the corresponding message is displayed
and if it is mixed in the middle of the title,
'Error: Invalid part '>', leading to id === parentId ('example-button-vue-docs'), inside title 'Example /Button/Vue <docs "/">'
It looks like this.