feat(db): Postgres schema, migrations and defects repository (T3)

Drizzle schema for projects, defects, push_subscriptions (C8); generated
migration; a defects repository (createDefect / listRecentDefects); a
programmatic migrator; and a db:verify script. section_id is a plain string
referencing in-code board ids, no FK (ADR 0001). Verified against real
Postgres: migration applies, a defect round-trips, /api/health reports db up.

server/db/client.ts

@@ -1,6 +1,9 @@
 import pg from 'pg'
+import { drizzle, type NodePgDatabase } from 'drizzle-orm/node-postgres'
+import * as schema from './schema'
 
 let pool: pg.Pool | undefined
+let db: NodePgDatabase<typeof schema> | undefined
 
 /** Lazily-created shared Postgres connection pool. */
 export function getPool(): pg.Pool {
@@ -10,6 +13,14 @@ export function getPool(): pg.Pool {
   return pool
 }
 
+/** Lazily-created Drizzle client bound to the shared pool. */
+export function getDb(): NodePgDatabase<typeof schema> {
+  if (!db) {
+    db = drizzle(getPool(), { schema })
+  }
+  return db
+}
+
 /** Liveness probe for the database, used by /api/health. */
 export async function checkDb(): Promise<'up' | 'down'> {
   try {