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/drizzle.config.ts

@@ -1,7 +1,7 @@
 import { defineConfig } from "drizzle-kit";
 
 export default defineConfig({
-  schema: "./src/schema/index.ts",
+  schema: "./src/schema/*.ts",
   out: "./src/migrations",
   dialect: "postgresql",
   dbCredentials: {