Add embedded PGlite support as zero-config database option

Add @electric-sql/pglite so the server can run without an external
Postgres instance. When DATABASE_URL is not set, the server auto-creates
an embedded PGlite database in ./data/pglite with schema push on startup.

- Add createPgliteDb() alongside the existing createDb()
- Make DATABASE_URL optional in server config
- Update drizzle config to glob schema files
- Update migrate script to support both Postgres and PGlite
- Add data/ to .gitignore for local PGlite storage

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

packages/db/package.json

@@ -14,12 +14,13 @@
     "seed": "tsx src/seed.ts"
   },
   "dependencies": {
+    "@electric-sql/pglite": "^0.3.15",
     "@paperclip/shared": "workspace:*",
     "drizzle-orm": "^0.38.4",
     "postgres": "^3.4.5"
   },
   "devDependencies": {
-    "drizzle-kit": "^0.30.4",
+    "drizzle-kit": "^0.31.9",
     "tsx": "^4.19.2",
     "typescript": "^5.7.3",
     "vitest": "^3.0.5"