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/poToken.ts

@@ -80,7 +80,11 @@ let mintWindow: BrowserWindow | null = null
  * Resolves with the token string on success, or null if the window was closed
  * by the user before extraction completed or if the field was not found.
  */
-export function openPoTokenWindow(): Promise<string | null> {
+export function openPoTokenWindow(
+  /** app-theme window background (UI23) — supplied by the IPC layer so this
+   *  window's chrome matches the app's Light/Dark instead of flashing white. */
+  backgroundColor?: string
+): Promise<string | null> {
   // If a minting window is already open, bring it to the front rather than
   // opening a second one.
   if (mintWindow && !mintWindow.isDestroyed()) {
@@ -105,6 +109,8 @@ export function openPoTokenWindow(): Promise<string | null> {
         width: 960,
         height: 640,
         title: 'AeroFetch — Fetch YouTube token',
+        // Match the app's resolved theme (UI23), like the cookie sign-in window.
+        backgroundColor,
         autoHideMenuBar: true,
         webPreferences: {
           partition: LOGIN_PARTITION,