macos: run as LSUIElement menubar app with NSStatusItem

Ship Lan Mouse on macOS as an accessory app (no Dock icon, no main
window on launch) with a status-bar item for show/quit. Closing the
window hides it instead of quitting so the menu bar stays the primary
surface.

- build-aux/macos-lsui-element.plist: LSUIElement=true plus
  NSInputMonitoringUsageDescription and NSAppleEventsUsageDescription
  (merged into Info.plist via cargo-bundle's osx_info_plist_exts).
- lan-mouse-gtk/src/macos_status_item.rs: NSStatusItem setup via raw
  objc_msgSend FFI. Loads a bundled 22pt PNG as a template image so
  it auto-tints for light/dark menu bars.
- scripts/makeicns.sh: emit Contents/Resources/menubar-template.png
  from the existing SVG.
- scripts/copy-macos-dylib.sh: flatten cargo-bundle's preserved
  target/ subdir under Resources so NSBundle pathForResource: finds
  the template image.
- lan-mouse-gtk/src/lib.rs: register the new modules, set up a
  Cmd+Q-wired quit action, configure bundle env vars (schemas,
  XDG_DATA_DIRS, GTK_DATA_PREFIX) when running from inside the .app,
  and filter the known upstream Gtk theme-parser warning spam.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -105,6 +105,7 @@ dnf install lan-mouse
 - Unzip it
 - Remove the quarantine with `xattr -rd com.apple.quarantine "Lan Mouse.app"`
 - Launch the app
+- Use the menu bar item to open the settings window or quit Lan Mouse. Bundled macOS builds run as a menu bar app and do not keep a Dock icon visible.
 - Grant accessibility permissions in System Preferences
 
 </details>
@@ -475,4 +476,4 @@ The following sections detail the emulation and capture backends provided by lan
 - `libei`: This backend uses [libei](https://gitlab.freedesktop.org/libinput/libei) and is supported by GNOME >= 45 or KDE Plasma >= 6.1.
 - `windows`: Backend for input capture on Windows.
 - `macos`: Backend for input capture on MacOS.
-- `x11`: TODO (not yet supported)
+- `x11`: TODO (not yet supported)