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>

.gitignore

@@ -6,3 +6,4 @@ drizzle/meta/
 .vite/
 coverage/
 .DS_Store
+data/