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/schema/activity_log.ts

@@ -0,0 +1,12 @@
+import { pgTable, uuid, text, timestamp, jsonb } from "drizzle-orm/pg-core";
+import { agents } from "./agents.js";
+
+export const activityLog = pgTable("activity_log", {
+  id: uuid("id").primaryKey().defaultRandom(),
+  action: text("action").notNull(),
+  entityType: text("entity_type").notNull(),
+  entityId: uuid("entity_id").notNull(),
+  agentId: uuid("agent_id").references(() => agents.id),
+  details: jsonb("details"),
+  createdAt: timestamp("created_at", { withTimezone: true }).notNull().defaultNow(),
+});