feat: optimize Modern.js 3.x documentation

[yimingjfe]

Summary

1. Update rspress

2. Add a link to Modern.js 2.0 in the navigation

3. Change the tutorials to examples

4. Hoist the documentation's directory

5. Use the new homepage UI

6. fix some dead links

Related Links

Checklist

• I have added changeset via pnpm run change.
• I have updated the documentation.
• I have added tests to cover my changes.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 55e9164

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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