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>

jobs/server-only.noop.cjs

@@ -0,0 +1,5 @@
+// Empty stand-in for the `server-only` package inside the worker runtime.
+// `server-only` throws when imported outside Next's RSC bundler; BullMQ workers
+// are legitimate server code running under plain Node/tsx, so we neutralize it.
+// Scoped to the worker process via jobs/bootstrap.ts — Next keeps the real guard.
+module.exports = {};