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/Home.vue

@@ -137,7 +137,7 @@ function openGameDetail(game: Game) {
         >
           <div class="game-cover-wrap">
             <img
-              :src="game.cover || '/game-placeholder.png'"
+              :src="game.cover || '/game-placeholder.svg'"
               :alt="game.name"
               class="game-cover"
             />