Add API server with routes, services, and middleware

Express server with CRUD routes for agents, goals, issues, projects,
and activity log. Includes validation middleware, structured error
handling, request logging, and health check endpoint with tests.

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

server/src/middleware/error-handler.ts

@@ -0,0 +1,18 @@
+import type { Request, Response, NextFunction } from "express";
+import { ZodError } from "zod";
+import { logger } from "./logger.js";
+
+export function errorHandler(
+  err: unknown,
+  _req: Request,
+  res: Response,
+  _next: NextFunction,
+) {
+  if (err instanceof ZodError) {
+    res.status(400).json({ error: "Validation error", details: err.errors });
+    return;
+  }
+
+  logger.error(err, "Unhandled error");
+  res.status(500).json({ error: "Internal server error" });
+}