docs(db): add introspect-only drizzle config and DB README

packages/db/drizzle.config.ts

@@ -0,0 +1,12 @@
+import { defineConfig } from "drizzle-kit";
+
+// INTROSPECT-ONLY. We never generate or push migrations against this database —
+// it is owned and written live by the game emulator. Use only `drizzle-kit pull`.
+export default defineConfig({
+  dialect: "mysql",
+  schema: "./src/schema/index.ts",
+  out: "./drizzle", // where `pull` writes the introspected schema snapshot
+  dbCredentials: {
+    url: process.env.DATABASE_URL ?? "",
+  },
+});