feat(ui): add custom title bar window controls for Windows and Linux

Hide the native title bar on win32/linux (titleBarStyle: 'hidden', frame
untouched so native resize borders and snapping keep working) and render
minimize / maximize-restore / close buttons in the renderer, mirroring the
existing macOS traffic-light setup.

- New WINDOW:* IPC contract (minimize, toggle-maximize, close, get-state)
  handled in window.events.ts, resolved from the sender WebContents;
  close goes through win.close() so window-bounds persistence still runs.
- WINDOW:STATE_CHANGED pushed on maximize/unmaximize/fullscreen so the
  maximize/restore glyph stays correct for OS-triggered changes; controls
  hide while fullscreen.
- WindowControlsComponent mounts once in app-root as a manual popover so
  it stays in the browser top layer above CDK overlays (dialogs,
  multi-EPG) - same behavior as macOS traffic lights.
- Theme-aware via CSS vars (--app-on-surface, --app-hover-overlay);
  Windows-red close hover. Drag regions get right padding through a
  body-level frameless-platform class.
- Gated by RuntimeCapabilitiesService.usesCustomWindowControls; PWA and
  macOS never mount the controls.

Includes unit specs for the component and IPC handlers, an Electron E2E
suite (window-controls.e2e.ts), and a window-chrome section in
docs/architecture/workspace-shell.md.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/web/src/app/app.component.html

@@ -1,3 +1,7 @@
 <router-outlet />
 
 <app-epg-progress-panel />
+
+@if (usesCustomWindowControls) {
+    <app-window-controls />
+}