feat(web/library): game library page — grid + custom-entry CRUD

Consumes the new library API (6351d51) via the orval-generated hooks. A poster grid
over GET /api/v1/library (all stores merged), plus create/edit/delete for custom
entries — the admin-UI half of "create custom entries via the web console".

- GameCard: portrait (600×900) art with an onError fallback chain portrait → header
  → text placeholder (many Steam titles lack a 600×900 capsule). A store badge marks
  Steam vs Custom; only custom cards expose edit/delete.
- Inline add/edit form (title + portrait/hero/header URLs + optional launch command,
  mapped to LaunchSpec{kind:"command"}) wired to useCreateCustomGame /
  useUpdateCustomGame / useDeleteCustomGame; the CRUD id strips the `custom:` prefix;
  every mutation invalidates the library query. QueryState handles load/empty/error.
- Nav entry (LibraryBig) + en/de i18n strings.

`bun run lint` (tsc) and `bun run build` both green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/messages/en.json

@@ -6,6 +6,7 @@
   "nav_host": "Host",
   "nav_clients": "Paired clients",
   "nav_pairing": "Pairing",
+  "nav_library": "Library",
   "nav_settings": "Settings",
   "status_title": "Live status",
   "status_video": "Video",
@@ -67,6 +68,25 @@
   "pairing_pending_age_secs": "{s}s ago",
   "pairing_pending_age_mins": "{min} min ago",
   "pairing_moonlight_title": "Moonlight (GameStream) pairing",
+  "library_title": "Library",
+  "library_empty": "No games found yet.",
+  "library_store_steam": "Steam",
+  "library_store_custom": "Custom",
+  "library_add_title": "Add a custom game",
+  "library_edit_title": "Edit custom game",
+  "library_add_button": "Add custom game",
+  "library_field_title": "Title",
+  "library_field_portrait": "Portrait art URL",
+  "library_field_hero": "Hero art URL",
+  "library_field_header": "Header art URL",
+  "library_field_command": "Launch command",
+  "library_field_command_help": "Optional. The command the host runs to launch this title.",
+  "library_save": "Save",
+  "library_create": "Add",
+  "library_cancel": "Cancel",
+  "library_edit": "Edit",
+  "library_delete": "Delete",
+  "library_delete_confirm": "Delete this custom game? This can't be undone.",
   "settings_title": "Settings",
   "settings_token_label": "API token",
   "settings_token_help": "Bearer token for the management API. Leave empty for a loopback host with no token.",