fix: remove unused imports for clean production build

Remove unused Wrench import from TaskLane, unused BranchMap import
and handleBranchSwitch from AssistantChatPage.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/pages/AssistantChatPage.tsx

@@ -8,7 +8,6 @@ import type { ForkMetadata, ActionItem, QuestionItem } from '@/types/ai-session'
 import { PageMeta } from '@/components/common/PageMeta'
 import { aiSessionsApi } from '@/api/aiSessions'
 import { useBranching } from '@/hooks/useBranching'
-import { BranchMap } from '@/components/session/BranchMap'
 import { analytics } from '@/lib/analytics'
 import { toast } from '@/lib/toast'
 import { ChatSidebar } from '@/components/assistant/ChatSidebar'
@@ -214,19 +213,6 @@ export default function AssistantChatPage() {
     toast.info('Pin feature coming soon')
   }
 
-  const handleBranchSwitch = async (branchId: string) => {
-    if (!activeChatId || loading) return
-    const result = await branching.switchBranch(activeChatId, branchId)
-    if (!result) return
-
-    // Load the branch's conversation into the chat
-    const branchMessages: MessageWithMeta[] = (result.conversation_messages || []).map(m => ({
-      role: m.role as 'user' | 'assistant',
-      content: m.content,
-    }))
-    setMessages(branchMessages)
-  }
-
   const handleSend = async () => {
     if (!input.trim() || !activeChatId || loading) return