fix: Multiple bug fixes and add auto-alias initialization

- Fix null-check in Users.tsx for user.accessKey filtering
- Fix null-check in Policies.tsx for policy.name filtering
- Add auto-initialization of default MinIO alias from env vars on startup
- Add validation to reject "undefined"/"null" as bucket names in browser API
- Server now creates DEFAULT_MINIO_ALIAS automatically if MINIO_ENDPOINT,
  MINIO_ACCESS_KEY, and MINIO_SECRET_KEY are provided

frontend/src/components/Policies/Policies.tsx

@@ -123,7 +123,7 @@ const Policies: React.FC = () => {
   };
 
   const filteredPolicies = policies.filter((policy) =>
-    policy.name.toLowerCase().includes(searchTerm.toLowerCase())
+    policy?.name?.toLowerCase().includes(searchTerm.toLowerCase())
   );
 
   const isBuiltInPolicy = (policyName: string) => {

frontend/src/components/Users/Users.tsx

@@ -96,7 +96,7 @@ const Users: React.FC = () => {
   };
 
   const filteredUsers = users.filter((user) =>
-    user.accessKey.toLowerCase().includes(searchTerm.toLowerCase())
+    user?.accessKey?.toLowerCase().includes(searchTerm.toLowerCase())
   );
 
   if (loading) {