feat: refactor daily task management with new pending tasks section

- Added `PendingTasksSection` to `DailyPageClient` for displaying uncompleted tasks.
- Implemented `getPendingCheckboxes` method in `DailyClient` and `DailyService` to fetch pending tasks.
- Introduced `getDaysAgo` utility function for calculating elapsed days since a date.
- Updated `TODO.md` to reflect the new task management features and adjustments.
- Cleaned up and organized folder structure to align with Next.js 13+ best practices.

src/app/api/daily/pending/route.ts

@@ -0,0 +1,29 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { dailyService } from '@/services/daily';
+import { DailyCheckboxType } from '@/lib/types';
+
+export async function GET(request: NextRequest) {
+  try {
+    const { searchParams } = new URL(request.url);
+    
+    const maxDays = searchParams.get('maxDays') ? parseInt(searchParams.get('maxDays')!) : undefined;
+    const excludeToday = searchParams.get('excludeToday') === 'true';
+    const type = searchParams.get('type') as DailyCheckboxType | undefined;
+    const limit = searchParams.get('limit') ? parseInt(searchParams.get('limit')!) : undefined;
+
+    const pendingCheckboxes = await dailyService.getPendingCheckboxes({
+      maxDays,
+      excludeToday,
+      type,
+      limit
+    });
+
+    return NextResponse.json(pendingCheckboxes);
+  } catch (error) {
+    console.error('Error fetching pending checkboxes:', error);
+    return NextResponse.json(
+      { error: 'Failed to fetch pending checkboxes' },
+      { status: 500 }
+    );
+  }
+}