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.

package.json

@@ -13,7 +13,8 @@
     "test:watch": "vitest",
     "typecheck": "nuxt typecheck",
     "db:generate": "drizzle-kit generate",
-    "db:migrate": "tsx server/db/migrate.ts"
+    "db:migrate": "tsx server/db/migrate.ts",
+    "db:verify": "tsx scripts/verify-db.ts"
   },
   "dependencies": {
     "drizzle-orm": "^0.45.2",