Implements org.kde.StatusNotifierWatcher as a D-Bus service so apps
like Nextcloud can register their tray icons. Icons are rendered from
SNI ARGB pixmaps (falling back to icon-name theme lookup), click calls
Activate(0,0), and NameOwnerChanged cleans up ghost icons when an app
exits. Styling follows the Bread Design System (4px tertiary radius,
xs/sm spacing, opacity transitions).
Also fixes a latent infinite-loop risk in osd.rs (.flatten → .map_while)
and syncs the notifications server version string to CARGO_PKG_VERSION.
