chore(fdroid): single-source fastlane metadata + reproducible-build prep

Make fastlane/metadata/android/ the single source of truth for store
listing metadata, consumed directly by the official F-Droid repo and
transformed into the self-hosted repo's localized layout at release time.

- Move fdroid-metadata/<appid>/<locale>/ -> fastlane/metadata/android/<locale>/
  (git-tracked renames: summary->short_description, description->full_description,
  + title.txt, images/icon.png, images/phoneScreenshots/); keep the app-level
  .yml control file for the self-hosted `fdroid update`.
- Add scripts/fastlane_to_fdroid_localized.sh (fastlane -> F-Droid localized,
  incl. changelogs) and scripts/sync_changelog_to_fastlane.sh (CHANGELOG.md ->
  fastlane changelog); verified byte-identical to the previous metadata.
- release.yaml: build self-hosted metadata from the fastlane tree and sync the
  per-version changelog before the transform (one changelog source for both
  channels).
- Disable AGP VCS-info embedding on release builds (vcsInfo { include = false })
  so builds reproduce byte-for-byte vs the distributed APK — the only file that
  otherwise differed (META-INF/version-control-info.textproto). Effective from
  the next release.
- Add docs/fdroid-official/ (draft fdroiddata recipe: reproducible build +
  AllowedAPKSigningKeys + Binaries + notes).
- Repoint README screenshots/icon, update docs/README + RELEASING, and skip the
  Android build on fastlane-only changes (ci.yaml).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/RELEASING.md

@@ -33,7 +33,15 @@ Published version codes so far: `v0.1.0`→100 … `v1.0.0`→10000 … `v2.0.0`
    the F-Droid per-version changelog.
 3. Bump the committed `versionName` (and `versionCode`) in
    `app/build.gradle.kts` to the new version. **This bump is what triggers the
-   release** when the branch merges to `main`.
+   release** when the branch merges to `main`. Then run
+   ```bash
+   scripts/sync_changelog_to_fastlane.sh
+   ```
+   and commit the generated
+   `fastlane/metadata/android/en-US/changelogs/<versionCode>.txt`. This is what
+   makes the **official** F-Droid repo show this version's changelog (it reads
+   the changelog from the tagged source tree). The self-hosted pipeline
+   regenerates it regardless, so forgetting only affects the official listing.
 4. **Verify the release build on a real device** — the mandatory gate. The
    shipped APK is R8-shrunk/obfuscated, and bugs that only appear there, or
    only on first run, never show up in the debug build or on a device that