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>

server/src/config.ts

@@ -1,16 +1,13 @@
 export interface Config {
   port: number;
-  databaseUrl: string;
+  databaseUrl: string | undefined;
   serveUi: boolean;
 }
 
 export function loadConfig(): Config {
-  const databaseUrl = process.env.DATABASE_URL;
-  if (!databaseUrl) throw new Error("DATABASE_URL is required");
-
   return {
     port: Number(process.env.PORT) || 3100,
-    databaseUrl,
+    databaseUrl: process.env.DATABASE_URL,
     serveUi: process.env.SERVE_UI === "true",
   };
 }