feat: initial commit — Curio mastery tutor

Full Next.js App Router application with:
- AI-graded lesson checkpoints (BKT/Elo mastery tracking)
- Auth.js v5: credentials, Google, GitHub, generic OIDC
- Anonymous-session-first with migrate-on-signin
- Admin panel: users, blueprints, reports, site settings
- Password reset + email verification (nodemailer/SMTP)
- Site config: require_auth + signups_enabled flags
- server-only guards on all DB/generation/verification modules
- PostgreSQL 16 + pgvector, Redis cache, Drizzle ORM
- 271 unit tests (Vitest), golden-eval harness, Playwright e2e stubs

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

.gitignore

@@ -0,0 +1,19 @@
+# dependencies
+node_modules
+.pnpm-store
+
+# Next.js
+.next
+out
+
+# environment
+.env.local
+.env*.local
+
+# drizzle — migrations and meta are committed (drizzle-kit needs the journal)
+
+# misc
+.DS_Store
+*.log
+npm-debug.log*
+pnpm-debug.log*