feat(images): report broken covers and achievement icons

README.md

@@ -40,6 +40,9 @@ To Be Played is split into three repositories:
 - **Public profile** at `/u/<display name>`, opt-in in the settings, with perfect games and average completion.
 - **Appearance**: accent color, corner style, wide layout, page background and banner from your own game art.
   Saved in Auth, so it follows you to every device.
+- **Broken pictures**: a Steam cover or achievement icon that does not load shows a placeholder and is reported
+  to Core once per page load (`POST /api/library/broken-images`, only with a session). Core repairs it at night;
+  a repaired cover comes back as `imageUrl`.
 - German and English, dark mode, mobile layout, session-expired message instead of a silent logout.
 - **Installable** as an app on phone and desktop (web app manifest, no service worker, so no offline mode).
 - **Session**: the tokens are HttpOnly cookies that no script can read. `apiFetch` renews an expired access token
@@ -83,6 +86,8 @@ flowchart LR
   Parallel requests and other tabs share this refresh (`navigator.locks`). When the second answer is still a
   `401`, the page calls `useSessionExpired`, which opens the login page. Public pages (landing page, public
   profile) use plain `fetch`.
+- `src/utils/brokenImages.js` reports pictures that fail to load (`GameCover`, achievement icons on the game
+  detail page) to Core.
 - `useLibrarySync` polls Core's `/api/library/sync-status` while a Steam sync runs, then loads the data again.
 
 ## Project structure