feat: ST-001–ST-005 foundation — scaffolding, Prisma, schema, seed, env

- ST-001: Next.js 16 + React 19 + TypeScript strict + Tailwind + shadcn/ui + all deps
- ST-002: Prisma v7 setup with better-sqlite3 adapter (local) and pg adapter (cloud)
- ST-003: Full schema migration (users, pbis, stories, sprints, tasks, todos, api_tokens)
- ST-004: Seed with 9 PBIs, ~40 stories, demo user (demo/demo1234), lars user
- ST-005: Zod-validated env vars, .env.example, lib/session, lib/auth, lib/api-auth

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/prisma.ts

@@ -0,0 +1,32 @@
+import { PrismaClient } from '@prisma/client'
+
+function createPrismaClient() {
+  const url = process.env.DATABASE_URL
+  if (!url) throw new Error('DATABASE_URL is not set')
+
+  if (url.startsWith('file:')) {
+    // SQLite (local development) — use better-sqlite3 adapter
+    const { PrismaBetterSqlite3 } = require('@prisma/adapter-better-sqlite3')
+    const adapter = new PrismaBetterSqlite3({ url })
+    return new PrismaClient({
+      adapter,
+      log: process.env.NODE_ENV === 'development' ? ['error', 'warn'] : ['error'],
+    })
+  }
+
+  // PostgreSQL (production) — use pg adapter
+  const { Pool } = require('pg')
+  const { PrismaPg } = require('@prisma/adapter-pg')
+  const pool = new Pool({ connectionString: url })
+  const adapter = new PrismaPg(pool)
+  return new PrismaClient({
+    adapter,
+    log: process.env.NODE_ENV === 'development' ? ['error', 'warn'] : ['error'],
+  })
+}
+
+const globalForPrisma = globalThis as unknown as { prisma: PrismaClient | undefined }
+
+export const prisma = globalForPrisma.prisma ?? createPrismaClient()
+
+if (process.env.NODE_ENV !== 'production') globalForPrisma.prisma = prisma