Release version management: single VERSION file as source of truth

- VERSION at repo root (0.1.2); bump it to cut a release
- App: generated AppVersion.kt (config-cache-safe Gradle task with
  VERSION as declared input) shown in Settings; sent to the gateway
  via X-Iris-App-Version header on the SSE open
- Gateway: reports its own version in hello.ack server_caps.app_version
  (read from the repo-root VERSION via the plugin symlink); stores the
  app's version in the device registry caps (merge, not overwrite, so
  an old app reconnecting without the header doesn't wipe it)
- Settings: app + gateway version rows, mismatch hint, and a best-effort
  Gitea latest-release check (ReleaseCheck) with an 'update available' hint
- Release workflow: reads VERSION from the repo (no manual input), with
  a guard against an empty file
- Docs: frames.schema.json + 04-wire-protocol.md updated for app_version

.gitea/workflows/release.yml

@@ -3,10 +3,8 @@ name: Release
 on:
   workflow_dispatch:
     inputs:
-      version:
-        description: "Release version (e.g. 0.2.0)"
-        required: true
-        type: string
+      # The release version comes from the repo-root VERSION file (the single
+      # source of truth) — bump it in a commit, then dispatch this workflow.
       changelog:
         description: "Release notes (markdown, shown on the release page). Single-line field — use literal \\n for line breaks."
         required: false
@@ -133,7 +131,8 @@ jobs:
 
       - name: Build APK + AAB
         run: |
-          VERSION=$(jq -r '.inputs.version' "$GITHUB_EVENT_PATH")
+          VERSION=$(cat "$GITHUB_WORKSPACE/VERSION")
+          [ -n "$VERSION" ] || { echo "::error::VERSION file is missing or empty"; exit 1; }
           cd app
           if [ -n "$ANDROID_KEYSTORE_FILE" ]; then
             # APK for direct sideloading, AAB for Play Store uploads.
@@ -155,7 +154,8 @@ jobs:
       # for it (jpackage picks the native type: msi on Windows, dmg on macOS).
       - name: Build desktop app-image + deb
         run: |
-          VERSION=$(jq -r '.inputs.version' "$GITHUB_EVENT_PATH")
+          VERSION=$(cat "$GITHUB_WORKSPACE/VERSION")
+          [ -n "$VERSION" ] || { echo "::error::VERSION file is missing or empty"; exit 1; }
           cd app
           # Self-contained app image (JRE bundled via jlink).
           ./gradlew :desktopApp:jpackage -PappVersion="$VERSION"
@@ -177,7 +177,7 @@ jobs:
           SERVER="${GITEA_SERVER_URL:-$GITHUB_SERVER_URL}"
           REPO="${GITEA_REPOSITORY:-$GITHUB_REPOSITORY}"
           TOKEN="${RELEASE_TOKEN:-$GITHUB_TOKEN}"
-          VERSION=$(jq -r '.inputs.version' "$GITHUB_EVENT_PATH")
+          VERSION=$(cat "$GITHUB_WORKSPACE/VERSION")
           # The dispatch input is a single-line field; turn literal \n into real newlines.
           CHANGELOG=$(jq -r '.inputs.changelog // ""' "$GITHUB_EVENT_PATH" | sed 's/\\n/\n/g')
           TAG="v$VERSION"