fix(server): add cors to modular routes

packages/server/test/routes-cors.test.ts

@@ -0,0 +1,17 @@
+import { describe, expect, test } from "bun:test"
+import { webHandler } from "../src/routes"
+
+describe("server CORS", () => {
+  test("adds CORS headers to /api/health 404 responses", async () => {
+    const response = await webHandler().handler(
+      new Request("http://localhost/api/health", {
+        method: "POST",
+        headers: { origin: "https://app.opencode.ai" },
+      }),
+    )
+
+    expect(response.status).toBe(404)
+    expect(response.headers.get("access-control-allow-origin")).toBe("https://app.opencode.ai")
+    expect(response.headers.get("vary")).toContain("Origin")
+  })
+})