feat: add system tray with quick actions and minimize-to-tray

System tray:
- Always-visible tray icon with context menu
- Quick Scratchpad action from tray (triggers session creation
  via IPC bridge to renderer)
- Running session count in tray tooltip and menu
- Click tray icon to show/focus window
- Quit option in tray menu

Minimize to tray:
- New 'Minimize to tray on close' toggle in Settings > Appearance
- When enabled, closing the window hides to tray instead of
  quitting (configurable per-user, default off)
- macOS: hides dock icon when minimized to tray
- Proper force-quit handling (Cmd+Q on macOS, tray Quit)

Full IPC contract chain:
- minimizeToTray setting in WorkspaceSettings
- setMinimizeToTray channel + ElectronApi method
- Preload bridge, service handler, IPC registration
- Preserved through workspace normalization

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/shared/domain/tooling.ts

@@ -65,6 +65,7 @@ export interface WorkspaceSettings {
   discoveredUserTooling: DiscoveredToolingState;
   terminalHeight?: number;
   notificationsEnabled?: boolean;
+  minimizeToTray?: boolean;
 }
 
 export interface SessionToolingSelection {
@@ -206,6 +207,8 @@ export function normalizeWorkspaceSettings(settings?: Partial<WorkspaceSettings>
     },
     discoveredUserTooling: normalizeDiscoveredToolingState(settings?.discoveredUserTooling),
     ...(terminalHeight !== undefined ? { terminalHeight } : {}),
+    ...(settings?.notificationsEnabled !== undefined ? { notificationsEnabled: settings.notificationsEnabled } : {}),
+    ...(settings?.minimizeToTray !== undefined ? { minimizeToTray: settings.minimizeToTray } : {}),
   };
 }