feat(audit): Batch 20 — Windows/main-process (UI23, W12, W15, L131)

UI23: cookie sign-in + PO-token windows open with the app's resolved
theme background (passed from the IPC layer), no more white flash.
W12: multi-resolution fallback tray icon (16/24/32/48 via
addRepresentation dataURL, embedded in trayFallbackIcons.ts); decode +
scale factors verified in an Electron probe.
W15: hardwareAcceleration setting (default false = software rendering);
index.ts gates disableHardwareAcceleration on it after the portable
redirect; Appearance card switch with restart note; boot path verified.
L131: resolved by-design — clearing the queue acknowledges failures;
flashFrame (W10) covers attention, Diagnostics persists the record.

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

src/main/settings.ts

@@ -289,6 +289,7 @@ function applySettings(s: Store<Settings>, partial: Partial<Settings>): void {
       case 'hasCompletedOnboarding':
       case 'minimizeToTray':
       case 'sidebarCollapsed':
+      case 'hardwareAcceleration':
         if (typeof value === 'boolean') s.set(key, value)
         break
       case 'launchAtStartup':