ci: add GitHub automation suite (Renovate, Release Please, Labeler, Danger, Actionlint)

[Himanth-reddy]

Summary

This PR sets up a comprehensive CI/CD automation suite:

• Renovate: Automated, grouped dependency updates for Gradle, npm, and GitHub Actions (.github/renovate.json).
• Release Please: Automated semantic release creation and changelog updates on push to main (.github/release-please-config.json).
• PR Labeler: Auto-labels PRs based on modified module paths (area: android, area: ios, area: web, area: backend, area: ci, documentation).
• Danger JS: Automated PR reviewer enforcing PR descriptions, lockfile updates, and WIP warnings (Dangerfile.js).
• Actionlint: Static workflow linting for all .github/workflows/*.yml files.

[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.