perf(frontend): Optimize component rendering with React.memo and hooks - Sprint 3 Story 2

Add React.memo to display components and useCallback/useMemo for better performance.

Changes:
- Added React.memo to TaskCard component
- Added React.memo to StoryCard component
- Added React.memo to KanbanBoard component
- Added React.memo to KanbanColumn component
- Added useCallback to kanban page drag handlers (handleDragStart, handleDragEnd)
- Added useCallback to epics page handlers (handleDelete, getStatusColor, getPriorityColor)
- Added useMemo for expensive computations in dashboard page (stats, recentProjects sorting)
- Added useMemo for total tasks calculation in KanbanBoard
- Removed unused isConnected variable from kanban page

Performance improvements:
- Reduced unnecessary re-renders in Card components
- Optimized list rendering performance with memoized callbacks
- Improved filtering and sorting performance with useMemo
- Better React DevTools Profiler metrics

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/(dashboard)/projects/[id]/kanban/page.tsx

@@ -8,7 +8,7 @@ import {
   DragStartEvent,
   closestCorners,
 } from '@dnd-kit/core';
-import { useState, useMemo } from 'react';
+import { useState, useMemo, useCallback } from 'react';
 import { useProjectStories } from '@/lib/hooks/use-stories';
 import { useEpics } from '@/lib/hooks/use-epics';
 import { useChangeStoryStatus } from '@/lib/hooks/use-stories';
@@ -43,7 +43,7 @@ export default function KanbanPage() {
 
   // SignalR real-time updates
   const queryClient = useQueryClient();
-  const { isConnected } = useSignalRConnection();
+  useSignalRConnection(); // Establish connection
   const changeStatusMutation = useChangeStoryStatus();
 
   // Subscribe to SignalR events for real-time updates
@@ -83,12 +83,12 @@ export default function KanbanPage() {
     Done: stories.filter((s) => s.status === 'Done'),
   }), [stories]);
 
-  const handleDragStart = (event: DragStartEvent) => {
+  const handleDragStart = useCallback((event: DragStartEvent) => {
     const story = stories.find((s) => s.id === event.active.id);
     setActiveStory(story || null);
-  };
+  }, [stories]);
 
-  const handleDragEnd = (event: DragEndEvent) => {
+  const handleDragEnd = useCallback((event: DragEndEvent) => {
     const { active, over } = event;
     setActiveStory(null);
 
@@ -101,7 +101,7 @@ export default function KanbanPage() {
       logger.debug(`[Kanban] Changing story ${story.id} status to ${newStatus}`);
       changeStatusMutation.mutate({ id: story.id, status: newStatus });
     }
-  };
+  }, [stories, changeStatusMutation]);
 
   if (isLoading) {
     return (