Fix profile save UX: close modal on success, refresh room members live

Saving a display name previously gave no feedback and left the modal
open, and an open room's message list/member panel kept showing the
pre-edit profile until reload -- both fetch that data from a member list
ChatShellPage only fetched once per room. Now the save closes the modal
(clear confirmation it worked) and ChatShellPage re-fetches room members
whenever the logged-in user's own display_name/avatar_filename changes,
so the update appears immediately everywhere without a reload.

frontend/src/components/ProfileModal.tsx

@@ -28,9 +28,9 @@ export function ProfileModal({ onClose }: ProfileModalProps) {
     try {
       const updated = await updateProfile(displayName.trim() || null)
       updateUser(updated)
+      onClose()
     } catch (err) {
       setError(err instanceof ApiError ? err.message : String(err))
-    } finally {
       setSavingName(false)
     }
   }