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.

media_server/tray.py

@@ -3,6 +3,7 @@
 import ctypes
 import io
 import logging
+import sys
 import webbrowser
 from pathlib import Path
 from typing import Callable
@@ -30,11 +31,24 @@ _IDYES = 6
 
 
 def _confirm(title: str, message: str) -> bool:
-    """Show a Yes/No dialog using native Windows MessageBox."""
-    result = ctypes.windll.user32.MessageBoxW(
-        0, message, title, _MB_YESNO | _MB_ICONQUESTION | _MB_TOPMOST | _MB_SETFOREGROUND
-    )
-    return result == _IDYES
+    """Show a Yes/No dialog before a destructive tray action.
+
+    Uses the native Windows MessageBox on win32; on Linux/macOS we don't
+    have a no-dependency GUI dialog available (Tk pulls in tkinter, gtk
+    pulls in PyGObject), so we log + auto-confirm — the tray menu items
+    themselves require a deliberate click already.
+    """
+    if sys.platform == "win32":
+        result = ctypes.windll.user32.MessageBoxW(
+            0,
+            message,
+            title,
+            _MB_YESNO | _MB_ICONQUESTION | _MB_TOPMOST | _MB_SETFOREGROUND,
+        )
+        return result == _IDYES
+
+    logger.info("Tray confirm (auto-yes on non-Windows): %s — %s", title, message)
+    return True
 
 
 def _create_icon_image(size: int = 64) -> Image.Image: