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

.gitignore

@@ -0,0 +1,15 @@
+node_modules
+.next
+dist
+.turbo
+*.tsbuildinfo
+.env
+.env.local
+.env.*.local
+coverage
+.DS_Store
+*.log
+__pycache__
+*.pyc
+.venv
+*.egg-info