Google Play is live: README + production track (#244)

Calendula is published on Google Play, so the pipeline and the docs stop treating it as pending.

**README**
- Google Play badge next to F-Droid/Obtainium, linking the store page.
- Install table: the Play row goes from "Coming soon / —" to a real channel.
- The "coming soon" section becomes a live one with the store link; the closed-testing "testers wanted" call drops out. The note that Play signs with Google's key (so switching channels needs an uninstall) stays, and the trailing shared-signing-key line now flags Play as the exception.

**Play track**
- Release uploads default to `production` instead of `internal` — in the lane (`fastlane/Fastfile`) and in the workflow default (`.gitea/workflows/release.yaml`). Merging a bumped versionName to main is already the human gate, so the manual Console promotion only added delay.
- `docs/RELEASING.md` updated to match, including the escape hatches (`PLAY_TRACK=internal` to stage, `PLAY_RELEASE_STATUS=draft` to hold).

Note: if a `PLAY_TRACK` repo variable is set on Gitea it still wins over the new default — needs checking there.

No issue for this one.

Co-authored-by: Jean-Luc Makiola <business@jeanlucmakiola.de>
Reviewed-on: https://codeberg.org/jlmakiola/calendula/pulls/244

.gitea/workflows/release.yaml

@@ -551,12 +551,11 @@ jobs:
     env:
       VERSION: ${{ needs.detect.outputs.version }}
       VERSION_CODE: ${{ needs.detect.outputs.version_code }}
-      # Where the bundle lands. `internal` by default so a release reaches
-      # testers rather than the public, and promotion to production stays a
-      # deliberate human action in the Play Console — the same posture as
-      # holding UI releases for on-device review. Override with the PLAY_TRACK
-      # repo variable once the flow is trusted.
-      PLAY_TRACK: ${{ vars.PLAY_TRACK || 'internal' }}
+      # Where the bundle lands. `production` — the release itself is already the
+      # gate (a bumped versionName only reaches main after on-device review), so
+      # a second manual promotion in the Play Console bought nothing but delay.
+      # Override with the PLAY_TRACK repo variable to stage a release instead.
+      PLAY_TRACK: ${{ vars.PLAY_TRACK || 'production' }}
       PLAY_RELEASE_STATUS: ${{ vars.PLAY_RELEASE_STATUS || 'completed' }}
       # Set PLAY_DRY_RUN=true to validate the edit against the API and discard
       # it instead of committing — used to rehearse the first upload.