Add Season Check page and dashboard card: per-lane readiness (season, study, lessons, highlights, feed); v2.20.0

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

server/routes/admin-dashboard.js

@@ -1,6 +1,7 @@
 import { Resend } from 'resend'
 import { readdir } from 'node:fs/promises'
 import { requireAdminAuth } from '../auth.js'
+import { buildSeasonCheck } from '../season-check.js'
 import { state } from '../state.js'
 import { getStorageStatus, loadUserProgress } from '../data.js'
 import { getStudyCatalog } from '../study-helpers.js'
@@ -219,7 +220,16 @@ export function register(app) {
         buildStudyProgress(), buildLatestEpisode(), buildNuggets(), buildHealth(), buildLastBroadcast(),
       ])
       const comments = state.studyComments ?? []
+      const seasonCheck = await buildSeasonCheck()
+        .then(c => ({
+          total: c.total,
+          errors: c.errors,
+          warnings: c.warnings,
+          lanes: c.lanes.map(l => ({ lane: l.lane, title: l.title, season: l.season, errors: l.errors, warnings: l.warnings })),
+        }))
+        .catch(() => null)
       res.json({
+        seasonCheck,
         trends: buildTrends(),
         traffic: buildTopTraffic(),
         reengagement: buildReengagement(),