feat: full feature buildout — streaming, i18n, mastery map, admin, jobs

Progressive lesson streaming via onSegment callback (fixes SSE for non-English
users — locale was shadowed in lesson-reader useEffect). Adds: BullMQ workers,
Redis stream buffer, token budget enforcement, Langfuse tracing, golden-eval
runner, Playwright e2e scaffolding, lesson depth/locale/preferences schema,
mastery map UI, admin panel (blueprints/users/reports/quality/misconceptions),
image queries, source citations, view transitions, reading animations, i18n
(next-intl), PDF export, surprise endpoint, and 402 passing unit tests.

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

next.config.ts

@@ -1,5 +1,10 @@
 import type { NextConfig } from 'next';
+import createNextIntlPlugin from 'next-intl/plugin';
 
-const nextConfig: NextConfig = {};
+const withNextIntl = createNextIntlPlugin('./src/i18n/request.ts');
 
-export default nextConfig;
+const nextConfig: NextConfig = {
+  serverExternalPackages: ['@react-pdf/renderer'],
+};
+
+export default withNextIntl(nextConfig);