feat: initial monorepo scaffold - Next.js 15 + Prisma + Python SDK stubs

- Turborepo monorepo with apps/web and packages/database, sdk-python
- Next.js 15 app with professional landing page (dark theme, emerald accent)
- Prisma schema: Trace, DecisionPoint, Span, Event models with full indexing
- Docker Compose: web (port 4200), postgres:16, redis:7, migrate service
- Python SDK package stubs: init, trace decorator, log_decision, integrations
- Multi-stage Dockerfile for standalone Next.js production build

apps/web/postcss.config.mjs

@@ -0,0 +1,6 @@
+const config = {
+  plugins: {
+    "@tailwindcss/postcss": {},
+  },
+};
+export default config;