feat: production-ready Linux & macOS support

- Add `linux` (dbus-python, PyGObject, python-xlib) and `macos`
  (pyobjc) extras to pyproject.toml with sys_platform markers; move
  cross-platform screen-brightness-control + monitorcontrol to base deps.
- build-dist-linux.sh: install `.[linux]`, pkg-config pre-flight for
  dbus-1/glib-2.0, emit a systemd unit with DBUS_SESSION_BUS_ADDRESS +
  XDG_RUNTIME_DIR + ReadWritePaths for ~/.config and ~/.cache so MPRIS
  works and audit-log / thumbnail writes aren't blocked by ProtectHome.
- New build-dist-macos.sh + per-user LaunchAgent installer producing
  MediaServer-vX.Y-macos-{arm64,x86_64}.tar.gz.
- Templated media-server.service updated to match the dist layout with
  proper session-bus env vars and a writable state-dir grant.
- install_linux.sh: drop dead requirements.txt path; install via
  `pip install ".[linux]"` and pre-create the writable state dirs.
- Cross-platform album artwork: abstract MediaController.get_album_art()
  with Linux (mpris:artUrl, file:// + http(s)://) and macOS (Spotify URL)
  impls; routes/media artwork endpoint now awaits the controller.
- LinuxMediaController connects to the session bus lazily — failure no
  longer crashes lifespan startup; MPRIS calls return idle until the bus
  is reachable. Logged once at INFO with a hint about
  `loginctl enable-linger`.
- Startup preflight on Linux warns if DBUS_SESSION_BUS_ADDRESS or
  XDG_RUNTIME_DIR is unset and informs the user when Wayland disables
  the foreground probe.
- /api/media/visualizer/status now reports a per-OS unavailable_reason.
- tray._confirm guarded against ctypes.windll on non-Windows.
- config.example.yaml: per-OS commented script examples; on_turn_off
  default is now a no-op echo (used to silently fail off Windows).
- README: replace stale `pip install -r requirements.txt` instructions
  with the new extras; add systemd lingering doc + troubleshooting
  section; add macOS LaunchAgent section.
- CI: new linux-smoke job (installs `.[linux]`, boots the server under
  dbus-run-session, asserts /api/health). Release workflow gains
  apt-deps step for the Linux build and a best-effort macOS build job.

.gitea/workflows/test.yml

@@ -34,3 +34,64 @@ jobs:
 
       - name: Test
         run: pytest --tb=short -q || test $? -eq 5
+
+  # Linux smoke test: install the linux extra in the same way build-dist-linux.sh
+  # does, then boot the server and hit /api/health. Catches dependency-resolution
+  # and import-time regressions for the Linux distribution path.
+  linux-smoke:
+    if: "!startsWith(github.event.head_commit.message, 'chore: release')"
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+
+      - name: Build frontend
+        run: npm ci && npm run build
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.11'
+
+      - name: Install Linux system deps for dbus-python + PyGObject
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y --no-install-recommends \
+            libdbus-1-dev libglib2.0-dev pkg-config \
+            libcairo2-dev libgirepository1.0-dev
+
+      - name: Install with linux extra
+        run: |
+          pip install --upgrade pip
+          pip install ".[linux]"
+
+      - name: Smoke — server boots and /api/health responds
+        run: |
+          # Headless Linux runners have no PulseAudio and no display
+          # server, so we disable the visualizer + update checker, and we
+          # use `dbus-run-session` to give LinuxMediaController a real
+          # session bus to talk to (otherwise dbus.SessionBus() would
+          # raise during startup). This isn't a full MPRIS integration
+          # test — it only proves the dispatcher selects the Linux
+          # controller, all imports resolve, and /api/health returns 200.
+          sudo apt-get install -y --no-install-recommends dbus-x11
+          export MEDIA_SERVER_VISUALIZER_ENABLED=false
+          export MEDIA_SERVER_UPDATE_CHECK_ENABLED=false
+          dbus-run-session -- bash -c '
+            python -m media_server.main --no-tray --port 18765 &
+            SERVER_PID=$!
+            for i in $(seq 1 30); do
+              if curl -sf "http://127.0.0.1:18765/api/health" >/dev/null; then
+                echo "Health check passed"
+                kill $SERVER_PID
+                wait $SERVER_PID 2>/dev/null || true
+                exit 0
+              fi
+              sleep 0.5
+            done
+            echo "Server did not respond within 15s"
+            kill $SERVER_PID 2>/dev/null || true
+            exit 1
+          '