feat: implement hybrid changesets workflow (mirror rnx-kit)

[Saadnajmi]

AI generated PR to mirror rnx-kit's publish workflow for FURN. Work in progress..

---

This commit implements a hybrid approach that mirrors rnx-kit's changesets workflow while keeping Azure Pipelines for NPM publishing.

Architecture:

• GitHub Actions: Version bump PR creation using @changesets/action
• Azure Pipelines: NPM publishing (compliance-friendly)
• GitHub App token: Bypasses org PR restrictions (like rnx-kit)

Changes:

• Add changesets dependencies (@changesets/cli, @changesets/changelog-github)
• Create .changeset/config.json (mirrors rnx-kit configuration)
• Create GitHub Actions workflow for version bumps
• Update Azure Pipelines to use 'changeset publish'
• Add comprehensive setup documentation

Key features:

• Uses official @changesets/action (battle-tested)
• Preserves dependency-profiles postbump hook
• Maintains Azure KeyVault integration for NPM token
• Keeps all 1ESPT compliance and security measures
• No prepublish hook needed (packages have proper exports field)

Setup required:

1. Configure GitHub App (react-native-sdk-bot or new app)
2. Add APP_ID variable and PRIVATE_KEY secret
3. See CHANGESETS_SETUP.md for detailed instructions

References:

• rnx-kit workflow pattern
• Plan: /Users/sanajmi/.claude/plans/stateless-jumping-unicorn.md

Platforms Impacted

• iOS
• macOS
• win32 (Office)
• windows
• android

Description of changes

(a summary of the changes made, often organized by file)

Verification

(how the change was tested, including both manual and automated tests)

Before	After
Screenshot or description before this change	Screenshot or description with this change

Pull request checklist

This PR has considered (when applicable):

• Automated Tests
• Documentation and examples
• Keyboard Accessibility
• Voiceover
• Internationalization and Right-to-left Layouts

[changeset-bot]

⚠️ No Changeset found

Latest commit: d790509

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.

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

💥 An error occurred when fetching the changed packages and changesets in this PR

Some errors occurred when validating the changesets config:
The package or glob expression "@fluentui-react-native/fluent-tester" is specified in the `ignore` option but it is not found in the project. You may have misspelled the package name or provided an invalid glob expression. Note that glob expressions must be defined according to https://www.npmjs.com/package/micromatch.
The package "@fluentui-react-native/dependency-profiles" depends on the ignored package "@fluentui-react-native/tester", but "@fluentui-react-native/dependency-profiles" is not being ignored. Please add "@fluentui-react-native/dependency-profiles" to the `ignore` option.