ci(release): split canary/stable tracks + unified Gitea Releases

A push to main publishes canary builds to canary channels (fast iteration,
unchanged); a single vX.Y.Z tag releases every platform at one version to the
stable channels and attaches all artifacts (.deb/.rpm/.msix/.apk/.aab/.dmg +
flatpak/decky/host-installer) to one Gitea Release. Collapses the
host-v*/win-v*/host-win-v* tag namespaces into v* — the channel split makes the
version-shadow bug structurally impossible (canary and stable are separate repos,
never a shared version line).

- scripts/ci/gitea-release.{sh,ps1}: one idempotent release helper
  (create-or-fetch + delete-before-upload), replacing 3 copy-pasted inline blocks
  and fixing their latent 409-on-reupload bug; prerelease flag auto-derived from
  the tag (an -rc tag won't shadow "Latest")
- channels: apt canary/stable distributions; rpm *-canary/base groups; flatpak
  canary/stable OSTree branches + a 2nd .Canary.flatpakref; generic-registry
  canary/ vs latest/ aliases; Play internal/alpha; Apple TestFlight vs notarized DMG
- android versionName threaded through gradle (versionCode stays run_number);
  Apple canary = TestFlight-only (no DMG/tvOS); canary base bumped to 0.3.0
- docs: new docs-site channels.md (subscribe table + cut-a-release runbook +
  box migration), refreshed ci.md workflow table + packaging READMEs

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

.gitea/workflows/docker.yml

@@ -58,16 +58,21 @@ jobs:
 
       - name: Build
         run: |
+          # On a release tag, also tag the image vX.Y.Z so a release pins reproducible web/docs images.
+          EXTRA=""
+          case "$GITHUB_REF" in refs/tags/v*) EXTRA="-t $REGISTRY/$OWNER/${{ matrix.image }}:${GITHUB_REF_NAME}" ;; esac
           docker build --pull ${{ matrix.buildargs }} \
             -f "${{ matrix.dockerfile }}" \
             -t "$REGISTRY/$OWNER/${{ matrix.image }}:latest" \
             -t "$REGISTRY/$OWNER/${{ matrix.image }}:sha-${GITHUB_SHA::8}" \
+            $EXTRA \
             "${{ matrix.context }}"
 
       - name: Push
         run: |
           docker push "$REGISTRY/$OWNER/${{ matrix.image }}:sha-${GITHUB_SHA::8}"
           docker push "$REGISTRY/$OWNER/${{ matrix.image }}:latest"
+          case "$GITHUB_REF" in refs/tags/v*) docker push "$REGISTRY/$OWNER/${{ matrix.image }}:${GITHUB_REF_NAME}" ;; esac
 
   # Deploy the docs site to unom-1, the DMZ services VM website/cms also deploy to
   # (docs.punktfunk.unom.io via Caddy on home-reverse-proxy-1 -> :3220). Same secret set