Add database package with Drizzle schema

Postgres schema via Drizzle ORM for agents, goals, issues, projects,
and activity log tables. Includes migration runner, seed script,
and Drizzle config.

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

packages/db/src/migrate.ts

@@ -0,0 +1,13 @@
+import { migrate } from "drizzle-orm/postgres-js/migrator";
+import postgres from "postgres";
+import { drizzle } from "drizzle-orm/postgres-js";
+
+const url = process.env.DATABASE_URL;
+if (!url) throw new Error("DATABASE_URL is required");
+
+const sql = postgres(url, { max: 1 });
+const db = drizzle(sql);
+
+await migrate(db, { migrationsFolder: new URL("./migrations", import.meta.url).pathname });
+await sql.end();
+console.log("Migrations complete");