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

tests/test_android.py

@@ -431,6 +431,61 @@ async def upload_file(
 # ── Lifecycle ───────────────────────────────────────────────────────────────
 
 
+@pytest.mark.asyncio
+async def test_hello_ack_advertises_app_version_and_sse_header_is_stored(
+    adapter, ws_client
+):
+    """hello.ack server_caps carries the gateway's release version, and the
+    app's X-Iris-App-Version header (sent on the SSE open) is stored in the
+    device registry's caps JSON (docs/04)."""
+    client, ack = ws_client
+    caps = ack["payload"]["server_caps"]
+    assert caps["app_version"] == sys.modules["iris_plugin_under_test"].version.plugin_version()
+
+    # The test client does not send the header; open a second SSE stream that
+    # does, and check the device registry picked it up.
+    from http.client import HTTPConnection
+
+    conn = HTTPConnection("127.0.0.1", adapter._http_server.bound_port, timeout=5)
+    conn.request(
+        "GET",
+        "/v1/events?cursor=0",
+        headers={
+            "Authorization": f"Bearer {TOKEN}",
+            "X-Iris-Device": DEVICE_ID,
+            "X-Iris-App-Version": "9.9.9",
+        },
+    )
+    resp = conn.getresponse()
+    assert resp.status == 200
+    resp.read(1)  # don't hold the stream
+    conn.close()
+
+    device = adapter._devices.get(DEVICE_ID)
+    assert device is not None
+    assert device["caps"].get("app_version") == "9.9.9"
+
+    # A reconnect from an OLD app build (no X-Iris-App-Version header) must
+    # NOT wipe the previously stored version — the caps merge preserves it.
+    conn2 = HTTPConnection("127.0.0.1", adapter._http_server.bound_port, timeout=5)
+    conn2.request(
+        "GET",
+        "/v1/events?cursor=0",
+        headers={
+            "Authorization": f"Bearer {TOKEN}",
+            "X-Iris-Device": DEVICE_ID,
+        },
+    )
+    resp2 = conn2.getresponse()
+    assert resp2.status == 200
+    resp2.read(1)
+    conn2.close()
+
+    device2 = adapter._devices.get(DEVICE_ID)
+    assert device2 is not None
+    assert device2["caps"].get("app_version") == "9.9.9"
+
+
 @pytest.mark.asyncio
 async def test_disconnect_broadcasts_status_restarting(adapter):
     """Teardown broadcasts ``status{state=restarting}`` before closing the