Checkpoint: Phase 13: Seed data for agents and orchestrator

- server/seed.ts: 6 default system agents (Orchestrator, Browser, Tool Builder, Agent Compiler, Coder, Researcher)
- Idempotent: runs only when agents table is empty
- Integrated into server/_core/index.ts startup
- server/seed.test.ts: 18 vitest tests, all pass
- Total: 69 tests pass (7 test files)

server/_core/index.ts

@@ -7,6 +7,7 @@ import { registerOAuthRoutes } from "./oauth";
 import { appRouter } from "../routers";
 import { createContext } from "./context";
 import { serveStatic, setupVite } from "./vite";
+import { seedDefaults } from "../seed";
 
 function isPortAvailable(port: number): Promise<boolean> {
   return new Promise(resolve => {
@@ -57,6 +58,9 @@ async function startServer() {
     console.log(`Port ${preferredPort} is busy, using port ${port} instead`);
   }
 
+  // Run idempotent seed on every startup (no-op if data already exists)
+  await seedDefaults();
+
   server.listen(port, () => {
     console.log(`Server running on http://localhost:${port}/`);
   });