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/group/GroupMembersPanel.vue

@@ -58,7 +58,7 @@ async function removeMember(userId: string, username: string) {
 
     <div class="members-list">
       <div v-for="member in members" :key="member.id" class="member-row">
-        <img :src="member.avatar || '/default-avatar.png'" class="member-avatar" alt="" />
+        <img :src="member.avatar || '/default-avatar.svg'" class="member-avatar" alt="" />
         <div class="member-info">
           <span class="member-name">{{ member.username }}</span>
           <span v-if="member.id === group.owner" class="owner-badge">群主</span>