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>

Cargo.toml

@@ -96,3 +96,5 @@ rdp_emulation = ["input-emulation/remote_desktop_portal"]
 name = "Lan Mouse"
 icon = ["target/icon.icns"]
 identifier = "de.feschber.LanMouse"
+osx_info_plist_exts = ["build-aux/macos-lsui-element.plist"]
+resources = ["target/menubar-template.png"]