Add per-episode play tracking with bar chart in admin analytics

- POST /api/analytics/play records a play event (title + date) on first
  play per player mount, skipping admin sessions
- Plays persisted to data/episode-plays.json with total + byDay buckets
- Admin stats response includes episodePlays sorted by total plays
- AnalyticsPanel shows horizontal bar chart + summary cards for all
  episodes dynamically — new episodes appear automatically as played

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

server/routes/analytics.js

@@ -6,7 +6,7 @@ import {
   MAX_RECENT_VISITS,
 } from '../config.js'
 import { state } from '../state.js'
-import { queueVisitorStatsWrite, queueHitStatsWrite, normalizeMessageType } from '../data.js'
+import { queueVisitorStatsWrite, queueHitStatsWrite, normalizeMessageType, recordEpisodePlay } from '../data.js'
 import {
   detectBot,
   sanitizeUserAgent,
@@ -146,6 +146,14 @@ export function register(app) {
     res.json({ ok: true, consent })
   })
 
+  app.post('/api/analytics/play', (req, res) => {
+    if (isValidAdminSession(req)) { res.json({ ok: false, reason: 'admin' }); return }
+    const title = typeof req.body?.title === 'string' ? req.body.title.trim().slice(0, 200) : ''
+    if (!title) { res.status(400).json({ ok: false, reason: 'missing-title' }); return }
+    recordEpisodePlay(title)
+    res.json({ ok: true })
+  })
+
   app.post('/api/analytics/pageview', async (req, res) => {
     if (isValidAdminSession(req)) {
       res.json({ ok: false, reason: 'admin' }); return
@@ -324,6 +332,14 @@ export function register(app) {
         users,
         funnel: { signups: funnelSignups, firstVisit: funnelFirstVisit, firstCompletion: funnelFirstCompletion },
       },
+      episodePlays: Object.entries(state.episodePlays)
+        .map(([title, data]) => ({
+          title,
+          total: data.total ?? 0,
+          byDay: data.byDay ?? {},
+          last30Days: buildLastNDaysStats(30).map(item => ({ day: item.day, plays: data.byDay?.[item.day] ?? 0 })),
+        }))
+        .sort((a, b) => b.total - a.total),
     })
   })
 }