fix(room): fix StrictMode reconnect loop, add revokeMessage rollback

- useEffect([wsClient]): remove wsClient from deps to prevent
  React StrictMode double-mount from disconnecting the real client.
  First mount connects client-1; StrictMode cleanup disconnects it.
  Second mount connects client-2; first mount's second cleanup would
  then disconnect client-2, leaving WS permanently unconnected.
  Changing to useEffect([]) + optional chaining fixes this.
- revokeMessage: add optimistic removal + rollback on server rejection,
  consistent with editMessage pattern. Previously a failed delete left the
  message visible with no feedback.

src/contexts/room-context.tsx

@@ -595,11 +595,17 @@ export function RoomProvider({
   }, [wsToken]);
 
   useEffect(() => {
-    if (!wsClientRef.current) return;
-    wsClientRef.current.connect().catch((e) => {
+    // NOTE: intentionally omitted [wsClient] from deps.
+    // In React StrictMode the component mounts twice — if wsClient were a dep,
+    // the first mount's effect would connect client-1, then StrictMode cleanup
+    // would disconnect it, then the second mount's effect would connect client-2,
+    // then immediately the first mount's *second* cleanup would fire and
+    // disconnect client-2 — leaving WS unconnected. Using a ref for the initial
+    // connect avoids this. The client is always ready by the time this runs.
+    wsClientRef.current?.connect().catch((e) => {
       console.error('[RoomContext] WS connect error:', e);
     });
-  }, [wsClient]);
+  }, []);
 
   const connectWs = useCallback(async () => {
     const client = wsClientRef.current;
@@ -899,10 +905,25 @@ export function RoomProvider({
     async (messageId: string) => {
       const client = wsClientRef.current;
       if (!client) return;
-      await client.messageRevoke(messageId);
-      setMessages((prev) => prev.filter((m) => m.id !== messageId));
-      // Persist to IndexedDB
-      deleteMessageFromIdb(messageId).catch(() => {});
+
+      // Optimistic removal: hide message immediately
+      let rollbackMsg: MessageWithMeta | null = null;
+      setMessages((prev) => {
+        rollbackMsg = prev.find((m) => m.id === messageId) ?? null;
+        return prev.filter((m) => m.id !== messageId);
+      });
+
+      try {
+        await client.messageRevoke(messageId);
+        deleteMessageFromIdb(messageId).catch(() => {});
+      } catch (err) {
+        // Rollback: restore message on server rejection
+        if (rollbackMsg) {
+          setMessages((prev) => [...prev, rollbackMsg!]);
+          saveMessage(rollbackMsg!).catch(() => {});
+        }
+        handleRoomError('Delete message', err);
+      }
     },
     [],
   );