feat: initial CodeBoard monorepo scaffold

Turborepo monorepo with npm workspaces:
- apps/web: Next.js 14 frontend with Tailwind v4, SSE progress, doc viewer
- apps/worker: BullMQ job processor (clone → parse → LLM generate)
- packages/shared: TypeScript types
- packages/parser: Babel-based AST parser (JS/TS) + regex (Python)
- packages/llm: OpenAI/Anthropic provider abstraction + prompt pipeline
- packages/diagrams: Mermaid architecture & dependency graph generators
- packages/database: Prisma schema (PostgreSQL)
- Docker multi-stage build (web + worker targets)

All packages compile successfully with tsc and next build.

turbo.json

@@ -0,0 +1,25 @@
+{
+  "$schema": "https://turbo.build/schema.json",
+  "globalDependencies": ["**/.env.*local"],
+  "tasks": {
+    "build": {
+      "dependsOn": ["^build"],
+      "inputs": ["$TURBO_DEFAULT$", ".env*"],
+      "outputs": [".next/**", "!.next/cache/**", "dist/**"]
+    },
+    "dev": {
+      "cache": false,
+      "persistent": true
+    },
+    "lint": {},
+    "clean": {
+      "cache": false
+    },
+    "db:generate": {
+      "cache": false
+    },
+    "db:push": {
+      "cache": false
+    }
+  }
+}