feat(site,docs): Tane is in F-Droid — link it next to Play

The inclusion MR was merged on 2026-07-25 and the app page went live on
2026-07-28 (v0.1.16, no antifeatures), so the landing page can finally
offer both stores.

- site: publish the F-Droid link and give each store link a single-colour
  icon, so the two are told apart by shape (play triangle vs. the
  free-software robot) rather than by brand colour. The badge row is a
  flex row now: left-aligned in the hero, centred under "Get Tane".
- README: an Install section with both stores, and a Status that matches
  reality (Block 1 shipped, Block 2 under way) instead of "early design".
- release.md: record that the app is published, that further releases only
  need a versionCode bump in the fdroiddata recipe, and that publication
  lags the green build by a day or two.
- open-decisions.md: log what unblocked inclusion — reproducible
  developer-signed builds, a Google-free APK, and opt-in networking.

README.md

@@ -9,9 +9,16 @@ The name honors the old Japanese mutual-aid traditions around rice — *yui* (sh
 - Web: https://tane.comunes.org
 - Package id: `org.comunes.tane`
 
+## Install
+
+Android, same signature in both stores — you can switch between them without reinstalling:
+
+- **F-Droid**: https://f-droid.org/packages/org.comunes.tane/ (reproducible, developer-signed build)
+- **Google Play**: https://play.google.com/store/apps/details?id=org.comunes.tane
+
 ## Status
 
-Early design. See [`PLAN.md`](PLAN.md) for the full analysis and roadmap (in Spanish). The valuable prior work lives in [`docs/mockups/`](docs/mockups/).
+Block 1 (inventory) is shipped and in beta; Block 2 (the social layer) is under way. See [`PLAN.md`](PLAN.md) for the full analysis and roadmap (in Spanish) and [`docs/design/open-decisions.md`](docs/design/open-decisions.md) for the live decision log. The valuable prior work lives in [`docs/mockups/`](docs/mockups/).
 
 ## Principles