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/vitest.config.ts

@@ -0,0 +1,7 @@
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  test: {
+    environment: "node",
+  },
+});