ci(release): support patch releases from release/* branches

- prepare-release: add `branch` input; validate branch/bump combination;
  skip Weblate merge, mobile build, and APK asset when not on main; point
  checkout, release target, and tag at the selected branch; backport the
  archived-versions.json entry to main via PR.
- build-mobile: gate Android release build and iOS TestFlight upload on
  `environment == production` instead of the branch name, so patch
  releases still produce production artifacts if ever re-enabled.
- docker: build on pushes to release/**; restrict retag-from-main jobs
  to PRs and main-branch pushes.
- docs-build: build on pushes to release/**; include release/** in the
  pre-job force-branches list.

.github/workflows/docs-build.yml

@@ -1,7 +1,7 @@
 name: Docs build
 on:
   push:
-    branches: [main]
+    branches: [main, 'release/**']
   pull_request:
   release:
     types: [published]
@@ -39,7 +39,7 @@ jobs:
           force-filters: |
             - '.github/workflows/docs-build.yml'
           force-events: 'release'
-          force-branches: 'main'
+          force-branches: 'main,release/**'
 
   build:
     name: Docs Build