Redesign admin dashboard with sidebar layout, planner overhaul, and readability fixes

- Replace horizontal top-nav with a dark sidebar (grouped: People / Academics / Tools)
- Add Dashboard landing page with kid stat cards, today's schedule, and recent scores
- Add /api/admin/schedule and /api/admin/recent-scores endpoints for dashboard data
- Add Lock button and mobile sidebar toggle in top bar
- Redesign planner toolbar: two-section layout (nav left, actions right)
- Elevate auto-schedule out of hidden accordion into always-visible inline bar
- Richer planner task cards: course color stripe, course name label, completion counter per day
- Dashed "＋ Add task" empty state instead of plain dash
- Fix nav-pill CSS conflict: student tabs (light bg) now use dark text; admin sidebar keeps white text
- Add seed.js demo data script for two students (Emma and Liam)

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

server.js

@@ -829,6 +829,24 @@ app.post('/api/parent/pin', requirePin, (req, res) => {
   res.json({ ok: true });
 });
 
+app.get('/api/admin/schedule', requirePin, (req, res) => {
+  const { date } = req.query;
+  const d = date || new Date().toISOString().slice(0, 10);
+  const rows = db.prepare(`SELECT * FROM schedule WHERE date = ? ORDER BY student_id, sort`).all(d);
+  res.json({ rows });
+});
+
+app.get('/api/admin/recent-scores', requirePin, (req, res) => {
+  const scores = db.prepare(`
+    SELECT s.id, s.student_id, i.title, s.score, s.total, s.submitted_at
+    FROM submissions s
+    JOIN items i ON i.id = s.item_id
+    ORDER BY s.submitted_at DESC
+    LIMIT 20
+  `).all();
+  res.json({ scores });
+});
+
 app.get('/api/admin/app-settings', requirePin, (req, res) => {
   res.json({
     school_name: getSetting('school_name') || '',