fix: allow authenticated users to search/view groups for joining

Changed groups collection listRule and viewRule from member-only to
any authenticated user, so users can find and join groups. Also
improved registration error messages with Chinese validation feedback.

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

backend/pb_migrations/1776421645_created_groups.js

@@ -84,8 +84,8 @@ migrate((db) => {
       }
     ],
     "indexes": [],
-    "listRule": "owner = @request.auth.id || members.id = @request.auth.id",
-    "viewRule": "owner = @request.auth.id || members.id = @request.auth.id",
+    "listRule": "@request.auth.id != \"\"",
+    "viewRule": "@request.auth.id != \"\"",
     "createRule": "@request.auth.id != \"\"",
     "updateRule": "owner = @request.auth.id",
     "deleteRule": "owner = @request.auth.id",