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.

packages/database/prisma/schema.prisma

@@ -0,0 +1,50 @@
+datasource db {
+  provider = "postgresql"
+  url      = env("DATABASE_URL")
+}
+
+generator client {
+  provider = "prisma-client-js"
+}
+
+model Generation {
+  id         String   @id @default(cuid())
+  repoUrl    String
+  repoName   String
+  commitHash String
+  status     Status   @default(QUEUED)
+  progress   Int      @default(0)
+  result     Json?
+  error      String?
+  costUsd    Float?
+  duration   Int?
+  createdAt  DateTime @default(now())
+  updatedAt  DateTime @updatedAt
+  userId     String?
+  user       User?    @relation(fields: [userId], references: [id])
+  viewCount  Int      @default(0)
+
+  @@unique([repoUrl, commitHash])
+  @@index([repoUrl])
+  @@index([status])
+}
+
+model User {
+  id          String       @id @default(cuid())
+  githubId    String       @unique
+  login       String
+  email       String?
+  avatarUrl   String?
+  createdAt   DateTime     @default(now())
+  generations Generation[]
+}
+
+enum Status {
+  QUEUED
+  CLONING
+  PARSING
+  GENERATING
+  RENDERING
+  COMPLETED
+  FAILED
+}