Automate Builds & Beta Distribution

Background: Native [platform] app with CI (11.1) and signing (11.2) in
place. I want to ship test builds to [TestFlight / Play internal/closed
testing / Firebase App Distribution] regularly.

Use case: Automate building, versioning, and distributing beta builds so
testers always get the latest without manual steps.

Implementation details:
- Fastlane lanes (or platform equivalents) for build → sign → upload
- Versioning strategy: build number auto-increment, marketing version,
  and tying builds to git commits/tags
- iOS: upload to TestFlight, manage groups, beta review for external
  testers. Android: upload an App Bundle to an internal/closed track.
- Generating changelogs/release notes for testers automatically
- Triggering on a tag or a manual CI button, not every commit

Deliverable: The automated distribution lanes/jobs, the versioning
scheme, the per-platform upload steps, the auto-changelog approach, and
the trigger strategy.