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.

package.json

@@ -0,0 +1,24 @@
+{
+  "name": "codeboard",
+  "private": true,
+  "workspaces": [
+    "apps/*",
+    "packages/*"
+  ],
+  "scripts": {
+    "dev": "turbo dev",
+    "build": "turbo build",
+    "lint": "turbo lint",
+    "clean": "turbo clean",
+    "db:generate": "turbo db:generate",
+    "db:push": "turbo db:push"
+  },
+  "devDependencies": {
+    "turbo": "^2",
+    "typescript": "^5.7"
+  },
+  "engines": {
+    "node": ">=20"
+  },
+  "packageManager": "npm@10.8.2"
+}