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/components/team/InvitationCard.vue

@@ -49,7 +49,7 @@ async function rejectInvitation() {
   <div class="invitation-card">
     <div class="invitation-header">
       <img
-        :src="invitation.expand?.from?.avatar || '/default-avatar.png'"
+        :src="invitation.expand?.from?.avatar || '/default-avatar.svg'"
         :alt="invitation.expand?.from?.username"
         class="avatar"
       />