feat: game cover file upload + fix game visibility rules

- Change game cover field from URL text to file upload (PocketBase migration)
- AddGameDialog now supports drag-and-drop image upload instead of URL input
- Add getGameCoverUrl() helper using pb.files.getUrl() for cover display
- Fix games listRule/viewRule: group.members.id syntax doesn't work in PB 0.22,
  changed to group.members ~ @request.auth.id for correct member visibility
- Update changelog with all v0.3.5 entries

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

backend/pb_migrations/1776938195_updated_games_cover_to_file.js

@@ -0,0 +1,51 @@
+/// <reference path="../pb_data/types.d.ts" />
+migrate((db) => {
+  const dao = new Dao(db)
+  const collection = dao.findCollectionByNameOrId("x5adjlc0txf16r8")
+
+  // remove old url cover field
+  collection.schema.removeField("cover_field")
+
+  // add new file cover field
+  collection.schema.addField(new SchemaField({
+    "system": false,
+    "id": "cover_file",
+    "name": "cover",
+    "type": "file",
+    "required": false,
+    "presentable": false,
+    "unique": false,
+    "options": {
+      "maxSelect": 1,
+      "maxSize": 5242880,
+      "mimeTypes": ["image/jpeg","image/png","image/gif","image/webp","image/svg+xml"],
+      "thumbs": null,
+      "protected": false
+    }
+  }))
+
+  return dao.saveCollection(collection)
+}, (db) => {
+  const dao = new Dao(db)
+  const collection = dao.findCollectionByNameOrId("x5adjlc0txf16r8")
+
+  // remove file cover field
+  collection.schema.removeField("cover_file")
+
+  // restore url cover field
+  collection.schema.addField(new SchemaField({
+    "system": false,
+    "id": "cover_field",
+    "name": "cover",
+    "type": "url",
+    "required": false,
+    "presentable": false,
+    "unique": false,
+    "options": {
+      "exceptDomains": null,
+      "onlyDomains": null
+    }
+  }))
+
+  return dao.saveCollection(collection)
+})