feat(config+ux): batch #5 — source maps, integration script, copy, redownload options

Clean config/copy items (Phase 7):
- L170: build.sourcemap 'hidden' on main/preload/renderer — emit .map for offline
  crash symbolication (of the CC8 logger's raw stacks) without exposing them.
- L34: add `test:integration` npm script (AEROFETCH_REAL_DOWNLOAD=1) for the opt-in
  real-download suite; stays out of `npm test` (needs network + live yt-dlp).
- L87: HistoryEntry carries the original `options`; redownload replays them so a
  re-download reproduces the same post-processing instead of the current defaults.
- L96: folder "Browse" buttons -> "Browse…" (they open the OS picker).
- L97: PO-token placeholder "(none)" -> "Optional -- paste a token" (consistent).
- Ticked already-resolved: L99 (M28 aria-label), L113 (UX2 tooltip=aria-label),
  L95 (usage follows verb/modifier rule), L172 (skipLibCheck accepted).

typecheck + 268 tests + eslint + prettier green (touched files LF/clean).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

electron.vite.config.ts

@@ -9,7 +9,11 @@ export default defineConfig({
       alias: {
         '@shared': resolve('src/shared')
       }
-    }
+    },
+    // Hidden source maps: emit .map files so a field crash stack (the logger writes
+    // raw stacks, CC8) can be symbolicated offline, without referencing/exposing them
+    // in the shipped bundle (L170).
+    build: { sourcemap: 'hidden' }
   },
   preload: {
     plugins: [externalizeDepsPlugin()],
@@ -21,6 +25,7 @@ export default defineConfig({
     // Emit CommonJS (.cjs): sandboxed preload scripts must be CJS, and enabling
     // the sandbox (webPreferences.sandbox) is part of the security hardening.
     build: {
+      sourcemap: 'hidden',
       rollupOptions: {
         output: {
           format: 'cjs',
@@ -36,6 +41,7 @@ export default defineConfig({
         '@shared': resolve('src/shared')
       }
     },
-    plugins: [react()]
+    plugins: [react()],
+    build: { sourcemap: 'hidden' }
   }
 })