fix(analytics): wire Grading Statistics card to real submission counts

Top Auto-graded / Pending Review / Total Graded tiles were hardcoded 0.
Add /api/auto-grade/grading-stats returning:
- autoGradedThisWeek: distinct submissions with AI-assisted marks in 7d
- pendingReview: submissions in submitted/grading/late status
- totalGraded: submissions in 'graded' status

AnalyticsTab now fetches and renders, with em-dash placeholders while
loading.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: WangYuTengg

src/client/features/staff-grading/components/AnalyticsTab.tsx

@@ -1,7 +1,25 @@
+import { useEffect, useState } from 'react';
+import { apiClient } from '../../../lib/api';
 import { CostAnalytics } from './CostAnalytics';
 import { QueueMonitor } from './QueueMonitor';
 
+type GradingStats = {
+  autoGradedThisWeek: number;
+  pendingReview: number;
+  totalGraded: number;
+};
+
 export function AnalyticsTab() {
+  const [stats, setStats] = useState<GradingStats | null>(null);
+  const [loading, setLoading] = useState(true);
+
+  useEffect(() => {
+    apiClient<GradingStats>('/api/auto-grade/grading-stats')
+      .then(setStats)
+      .catch(console.error)
+      .finally(() => setLoading(false));
+  }, []);
+
   return (
     <div className="space-y-6">
       {/* Statistics */}
@@ -10,17 +28,23 @@ export function AnalyticsTab() {
         <div className="grid grid-cols-1 md:grid-cols-3 gap-4">
           <div className="bg-green-50 border border-green-200 rounded-lg p-4">
             <p className="text-sm text-green-600 font-medium mb-1">Auto-graded</p>
-            <p className="text-3xl font-bold text-green-900">0</p>
+            <p className="text-3xl font-bold text-green-900">
+              {loading ? '—' : stats?.autoGradedThisWeek ?? 0}
+            </p>
             <p className="text-xs text-green-700 mt-1">submissions this week</p>
           </div>
           <div className="bg-yellow-50 border border-yellow-200 rounded-lg p-4">
             <p className="text-sm text-yellow-600 font-medium mb-1">Pending Review</p>
-            <p className="text-3xl font-bold text-yellow-900">0</p>
+            <p className="text-3xl font-bold text-yellow-900">
+              {loading ? '—' : stats?.pendingReview ?? 0}
+            </p>
             <p className="text-xs text-yellow-700 mt-1">submissions waiting</p>
           </div>
           <div className="bg-blue-50 border border-blue-200 rounded-lg p-4">
             <p className="text-sm text-blue-600 font-medium mb-1">Total Graded</p>
-            <p className="text-3xl font-bold text-blue-900">0</p>
+            <p className="text-3xl font-bold text-blue-900">
+              {loading ? '—' : stats?.totalGraded ?? 0}
+            </p>
             <p className="text-xs text-blue-700 mt-1">all time</p>
           </div>
         </div>

src/server/routes/auto-grade/grading-stats.ts

@@ -0,0 +1,55 @@
+import { Hono } from 'hono';
+import { and, eq, gte, sql } from 'drizzle-orm';
+import { db } from '../../../db/index.js';
+import { submissions, marks } from '../../../db/schema.js';
+import { authMiddleware, type AuthContext } from '../../middleware/auth.js';
+import { getErrorMessage } from '../../lib/error-utils.js';
+
+const gradingStatsRoute = new Hono<AuthContext>();
+
+/**
+ * GET /api/auto-grade/grading-stats
+ *
+ * Returns top-line submission grading counts for the staff Analytics tab:
+ * - autoGradedThisWeek: distinct submissions that received any AI-assisted mark in the last 7 days
+ * - pendingReview: submissions awaiting human review (status submitted/grading)
+ * - totalGraded: all-time count of submissions in 'graded' status
+ */
+gradingStatsRoute.get('/grading-stats', authMiddleware, async (c) => {
+  const user = c.get('user');
+
+  if (!user || (user.role !== 'staff' && user.role !== 'admin')) {
+    return c.json({ error: 'Unauthorized' }, 403);
+  }
+
+  try {
+    const sevenDaysAgo = new Date();
+    sevenDaysAgo.setDate(sevenDaysAgo.getDate() - 7);
+
+    const [autoGradedRow] = await db
+      .select({ value: sql<number>`COUNT(DISTINCT ${marks.submissionId})::int` })
+      .from(marks)
+      .where(and(eq(marks.isAiAssisted, true), gte(marks.createdAt, sevenDaysAgo)));
+
+    const [pendingRow] = await db
+      .select({ value: sql<number>`COUNT(*)::int` })
+      .from(submissions)
+      .where(sql`${submissions.status} IN ('submitted', 'grading', 'late')`);
+
+    const [totalRow] = await db
+      .select({ value: sql<number>`COUNT(*)::int` })
+      .from(submissions)
+      .where(eq(submissions.status, 'graded'));
+
+    return c.json({
+      autoGradedThisWeek: autoGradedRow?.value ?? 0,
+      pendingReview: pendingRow?.value ?? 0,
+      totalGraded: totalRow?.value ?? 0,
+    });
+  } catch (error: unknown) {
+    console.error('Grading stats error:', error);
+    return c.json({ error: 'Failed to fetch grading stats', details: getErrorMessage(error) }, 500);
+  }
+});
+
+export default gradingStatsRoute;

src/server/routes/auto-grade/index.ts

@@ -8,6 +8,7 @@ import acceptRoute from './accept.js';
 import rejectRoute from './reject.js';
 import assignmentsRoute from './assignments.js';
 import batchAcceptRoute from './batch-accept.js';
+import gradingStatsRoute from './grading-stats.js';
 
 const autoGrade = new Hono<AuthContext>();
 
@@ -19,5 +20,6 @@ autoGrade.route('/', acceptRoute);
 autoGrade.route('/', rejectRoute);
 autoGrade.route('/', assignmentsRoute);
 autoGrade.route('/', batchAcceptRoute);
+autoGrade.route('/', gradingStatsRoute);
 
 export default autoGrade;