feat(shell): startup window mode, --fullscreen switch and F11 toggle (#1514)

Settings > General gains "Window on startup" (normal / maximized /
fullscreen), Electron only, mirrored into the main-process config by
SETTINGS_UPDATE and applied at the next window creation. `--fullscreen`
forces one fullscreen launch (consumed by the first window). F11 toggles
OS-level fullscreen through WINDOW:TOGGLE_FULLSCREEN — the exit path on
Windows/Linux where the title bar is hidden — and is skipped while the
player owns document.fullscreenElement.

attachWindowStateEvents tracks native and HTML fullscreen as two flags,
since Electron leaves only the HTML state when the window was already
natively fullscreen. macOS ignores the constructor `fullscreen` option on a
hidden window, so ready-to-show repeats the request after show(). Toggles
are decided by an observe-only, event-fed tracker
(native-fullscreen-transitions.ts), never against isFullScreen().

Closes #1455

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

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

@@ -110,6 +110,8 @@
                         [themeOptions]="themeOptions"
                         [coverSizeOptions]="coverSizeOptions"
                         [startupBehaviorOptions]="startupBehaviorOptions"
+                        [startupWindowModeOptions]="startupWindowModeOptions"
+                        [supportsStartupWindowMode]="supportsStartupWindowMode"
                         (selectTheme)="form.selectTheme($event)"
                         (selectCoverSize)="form.selectCoverSize($event)"
                     />