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/shared/ipc.ts

@@ -624,6 +624,14 @@ export interface Settings {
   launchAtStartup: boolean
   /** whether the navigation sidebar is collapsed to icon-only mode */
   sidebarCollapsed: boolean
+  /**
+   * Opt in to GPU compositing (W15; takes effect on next launch). Off by
+   * default: software rendering is the safe choice for this app's target
+   * hardware — on some old/locked-down GPUs (the documented GeForce GT 625
+   * case) Chromium's GPU compositor paints the whole window blank. Users on
+   * modern GPUs can turn this on for smoother high-DPI/large-window rendering.
+   */
+  hardwareAcceleration: boolean
   /**
    * Optional Gitea access token for the in-app updater. Empty = anonymous (works
    * only where the release repo allows anonymous access). When the release repo
@@ -689,6 +697,7 @@ export const DEFAULT_SETTINGS: Settings = {
   minimizeToTray: false,
   launchAtStartup: false,
   sidebarCollapsed: false,
+  hardwareAcceleration: false,
   updateToken: ''
 }