feat(db): add PostgreSQL connection, migration runner, and seed data

- Add pool export and graceful shutdown hook to db/index.ts
- Create migrate.ts — programmatic migration runner using drizzle-orm/migrator
- Create seed.ts — idempotent seed script with sample users, subscriptions,
  watchlist items, exposures, alerts, blog posts, properties, and removal requests
- Create db.test.ts — unit tests for db, migrate, and seed module exports
- Add web/.env.example documenting DATABASE_URL
- Add db:generate, db:push, db:migrate, db:seed scripts to web/package.json

web/package.json

@@ -7,7 +7,11 @@
     "start": "vite start",
     "preview": "vite preview",
     "test": "vitest run",
-    "lint": "tsc --noEmit"
+    "lint": "tsc --noEmit",
+    "db:generate": "drizzle-kit generate",
+    "db:push": "drizzle-kit push",
+    "db:migrate": "tsx src/server/db/migrate.ts",
+    "db:seed": "tsx src/server/db/seed.ts"
   },
   "dependencies": {
     "@solidjs/meta": "^0.29.4",
@@ -34,6 +38,7 @@
     "@types/pg": "^8.20.0",
     "drizzle-kit": "^0.31.10",
     "jsdom": "^29.1.1",
+    "tsx": "^4.22.3",
     "vite-plugin-solid": "^2.11.12",
     "vitest": "^4.1.5"
   }