fix(chat): handle user object from API responses

- Updated sendMessage.fulfilled to extract user.name from nested user object
- Updated fetchChatHistory.fulfilled to transform API format to internal format
- API response: { user: { name: "..." }, user_id: "..." }
- Internal format: { senderName: "...", senderId: "..." }
- WebSocket messages already use user_name (unchanged)

Fixes 'Unknown' sender name for messages from API (send + fetch).

jam-ui/src/store/features/sessionChatSlice.js

@@ -229,9 +229,21 @@ const sessionChatSlice = createSlice({
           state.messagesByChannel[channel] = [];
         }
 
+        // Transform API response format to internal format
+        // API returns: { user: { name: "..." }, user_id: "...", ... }
+        // Internal format: { senderName: "...", senderId: "...", ... }
+        const transformedMessages = messages.map(m => ({
+          id: m.id,
+          senderId: m.user_id,
+          senderName: m.user?.name || 'Unknown',
+          message: m.message,
+          createdAt: m.created_at,
+          channel: m.channel
+        }));
+
         // Deduplicate messages
         const existingIds = new Set(state.messagesByChannel[channel].map(m => m.id));
-        const newMessages = messages.filter(m => !existingIds.has(m.id));
+        const newMessages = transformedMessages.filter(m => !existingIds.has(m.id));
 
         // Prepend new messages (oldest first for pagination)
         state.messagesByChannel[channel] = [...newMessages, ...state.messagesByChannel[channel]];
@@ -285,8 +297,8 @@ const sessionChatSlice = createSlice({
           if (index !== -1) {
             messages[index] = {
               id: realMessage.id,
-              senderId: realMessage.sender_id,
-              senderName: realMessage.sender_name,
+              senderId: realMessage.user_id,
+              senderName: realMessage.user?.name || 'Unknown',
               message: realMessage.message,
               createdAt: realMessage.created_at,
               channel: realMessage.channel