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/components/assistant/TaskLane.tsx

@@ -1,8 +1,7 @@
 import { useState, useEffect, useRef, useCallback } from 'react'
 import {
   Copy, Check, SkipForward, Terminal, ChevronDown, ChevronUp,
-  Send, Clipboard, Loader2, X, MessageCircleQuestion, Wrench,
-  Eye,
+  Send, Clipboard, Loader2, X, MessageCircleQuestion, Eye,
 } from 'lucide-react'
 import { cn } from '@/lib/utils'
 import { toast } from '@/lib/toast'