fix(frontend/autopilot): improve AutoPilot OS push notification icon and copy (#13231)

### Why / What / How

**Why:** The OS-level push notification fired by AutoPilot on session
completion looks broken next to other apps on iOS (and Android): the
icon is the 16×16 `favicon.ico` upscaled by the OS, so it renders
blurry/pixelated, and the copy ("A response is waiting for you.") is
wordier than the rest of our notification surface area.

**What:** Adds a dedicated high-resolution square notification icon, and
tightens the copy to match the design mockup — title `AutoGPT`, body
`Task completed` (and `Task failed` for the parallel failure case).

**How:** The push payload from the backend only carries `{type, event,
session_id, status}` — title/body/icon are hardcoded in the service
worker (`public/push-sw.js`). So this is a frontend-only change:
- Drop the new `notification-icon-192.png` (light-on-dark AutoGPT mark)
into `public/`, plus a 512×512 for retina/Android upscaling.
- Swap `icon` and `badge` in `push-sw.js` away from `/favicon.ico`.
- Update the `NOTIFICATION_MAP` entries for
`copilot_completion.session_completed` and `session_failed`.
- Mirror the same values in the in-page `Notification()` fallback in
`useCopilotNotifications.ts` (used when no SW push subscription is
active).
- Update `push-sw-helpers.test.ts` assertions accordingly.

### Changes 🏗️

- `frontend/public/notification-icon-192.png`,
`notification-icon-512.png` — new square brand icon assets
(light-on-dark)
- `frontend/public/push-sw.js` — new title/body strings, icon/badge
point at the new PNG
- `frontend/src/app/(platform)/copilot/useCopilotNotifications.ts` —
in-page fallback notification updated to match
-
`frontend/src/services/push-notifications/__tests__/push-sw-helpers.test.ts`
— assertions updated, added body asserts

Closes
[OPEN-3139](https://linear.app/autogpt/issue/OPEN-3139/fixfrontendautopilot-improve-autopilot-os-push-notification-icon-and).

### Checklist 📋

#### For code changes:
- [x] I have clearly listed my changes in the PR description
- [x] I have made a test plan
- [ ] I have tested my changes according to the test plan:
- [x] `pnpm test:unit` for `src/services/push-notifications` (73/73
pass)
  - [x] `pnpm test:unit` for `src/app/(platform)/copilot` (972/972 pass)
  - [x] `pnpm format`, `pnpm lint`, `pnpm types` all clean
- [ ] **Manual:** trigger a real AutoPilot session-completion on iOS
Safari/PWA, confirm the notification renders the new icon crisply and
reads "AutoGPT — Task completed"
- [ ] **Manual:** same on Android Chrome — confirm icon is clear and the
status-bar badge silhouette looks correct
- [ ] **Manual:** trigger a session failure and confirm "Task failed"
copy

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Co-authored-by: Nicholas Tindle <nicholas.tindle@agpt.co>