ci: add PR labeler and Actionlint automation

[Himanth-reddy]

Summary

• Adds automatic PR area labels based on changed paths.
• Adds Actionlint validation for GitHub workflow files.
• Stops ignoring .github/workflows/ so new workflow files can be tracked.

Review changes

• Renovate, Release Please, and Danger were removed as requested.
• Rebased onto current main while preserving the current build/signing workflow.
• Added the configured area:* labels to the repository without increasing workflow permissions.

Validation

• All workflow files pass Actionlint locally.

[ProdigyV21]

Thanks — the config quality is careful (labeler globs match our real layout, the release-please manifest matches the latest tag, and the SC2129 cleanup shows you ran actionlint against the repo). Actionlint and the labeler are welcome.

Three pieces can't go in:

1. Renovate: there's no RENOVATE_TOKEN secret, and the GITHUB_TOKEN fallback can't initialize self-hosted Renovate — the Saturday cron would fail every week. Even with a PAT, Renovate's PRs wouldn't trigger build-check, so dependency bumps (AGP/Compose/Next) would land with zero CI. The config also uses deprecated matchPaths/matchPackagePatterns.

2. Release Please: release-type simple only maintains version.txt/CHANGELOG — it can't bump versionName in app/build.gradle.kts (the real APK version), and web's version.json is a build-generated stamp that's never committed. Its first feat commit would also propose v1.10.0, breaking the 1.9.98x scheme. We deliberately removed release automation in 1be6064, and this opens a release PR on every push to main.

3. Danger: a summary comment on every PR is noise at two-person scale — drop it, or warns-only without the comment.

Mergeable version: remove renovate.yml + renovate.json, release-please.yml + both configs, and danger.yml + Dangerfile.js; keep actionlint, labeler, the build-check cleanup, and the .gitignore change. Happy to merge that.

The requested removal of Renovate, Release Please, and Danger has been completed. The branch was also rebased onto current main, the CI conflict was resolved by preserving main's build/signing workflow, and all checks now pass.

[ProdigyV21]

Requested changes are addressed, the branch is current with main, and Actionlint plus the Android build both pass.