feat: Payload CMS robustness - auto-detect migrations, deep health check, improved error messages

- cms-sync.sh: auto-detect migrations from src/migrations/*.ts (no manual list)
- cms-sync.sh: pre-flight container checks with actionable error messages
- api/health/cms: deep health check that queries all Payload collections
- deploy.yml: auto-detect migrations in sanitization step
- deploy.yml: CMS deep health smoke test in post-deploy

app/api/health/cms/route.ts

@@ -1,9 +1,41 @@
 import { NextResponse } from 'next/server';
+import { getPayload } from 'payload';
+import configPromise from '@payload-config';
 
 export const dynamic = 'force-dynamic';
 
+/**
+ * Deep CMS Health Check
+ * Validates that Payload CMS can actually query the database.
+ * Used by post-deploy smoke tests to catch migration/schema issues.
+ */
 export async function GET() {
-  // Payload is embedded within the Next.js app, so if this route responds, the CMS is up.
-  // Further DB health checks can be implemented via Payload Local API later.
-  return NextResponse.json({ status: 'ok', message: 'Payload CMS is embedded.' }, { status: 200 });
+  const checks: Record<string, string> = {};
+
+  try {
+    const payload = await getPayload({ config: configPromise });
+    checks.init = 'ok';
+
+    // Verify each collection can be queried (catches missing locale tables, broken migrations)
+    const collections = ['posts', 'products', 'pages', 'media'] as const;
+    for (const collection of collections) {
+      try {
+        await payload.find({ collection, limit: 1, locale: 'en' });
+        checks[collection] = 'ok';
+      } catch (e: any) {
+        checks[collection] = `error: ${e.message?.substring(0, 100)}`;
+      }
+    }
+
+    const hasErrors = Object.values(checks).some(v => v.startsWith('error'));
+    return NextResponse.json(
+      { status: hasErrors ? 'degraded' : 'ok', checks },
+      { status: hasErrors ? 503 : 200 },
+    );
+  } catch (e: any) {
+    return NextResponse.json(
+      { status: 'error', message: e.message?.substring(0, 200), checks },
+      { status: 503 },
+    );
+  }
 }