feat: add game library CRUD/import/export/favorites/comments, fix team creation

- Game library: add/delete games per group, JSON/CSV import/export, favorites, star ratings & comments
- Fix team session creation: add creator to members array, handle null currentGroup
- Fix image loading: rename SVG files from .png to .svg extensions
- Add PocketBase migrations for game_comments and game_favorites collections
- Remove seed data script

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/views/Layout.vue

@@ -106,7 +106,7 @@ function goHome() {
         </div>
         <div class="user-info">
           <img
-            :src="userStore.user?.avatar || '/default-avatar.png'"
+            :src="userStore.user?.avatar || '/default-avatar.svg'"
             class="user-avatar"
             alt=""
           />