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

turbo.json

@@ -0,0 +1,17 @@
+{
+  "$schema": "https://turbo.build/schema.json",
+  "globalDependencies": ["**/.env.*local"],
+  "tasks": {
+    "build": {
+      "dependsOn": ["^build"],
+      "inputs": ["$TURBO_DEFAULT$", ".env*"],
+      "outputs": [".next/**", "!.next/cache/**", "dist/**"]
+    },
+    "dev": { "cache": false, "persistent": true },
+    "lint": {},
+    "clean": { "cache": false },
+    "db:generate": { "cache": false },
+    "db:migrate": { "cache": false },
+    "db:push": { "cache": false }
+  }
+}