refactor: add afterEach cleanup to all gateway tests

Added afterEach hooks with server/ws cleanup to:
- server.channels.test.ts (3 tests)
- server.config-apply.test.ts (2 tests)
- server.sessions-send.test.ts (already had this)

This ensures ports are properly released between tests, preventing
timeout issues from port conflicts.

src/gateway/server.config-apply.test.ts

@@ -1,7 +1,7 @@
 import fs from "node:fs/promises";
 import os from "node:os";
 import path from "node:path";
-import { describe, expect, it, vi } from "vitest";
+import { afterEach, describe, expect, it, vi } from "vitest";
 
 import {
   connectOk,
@@ -12,9 +12,26 @@ import {
 
 installGatewayTestHooks();
 
+const servers: Array<Awaited<ReturnType<typeof startServerWithClient>>> = [];
+
+afterEach(async () => {
+  for (const { server, ws } of servers) {
+    try {
+      ws.close();
+      await server.close();
+    } catch {
+      /* ignore */
+    }
+  }
+  servers.length = 0;
+  await new Promise((resolve) => setTimeout(resolve, 50));
+});
+
 describe("gateway config.apply", () => {
   it("writes config, stores sentinel, and schedules restart", async () => {
-    const { server, ws } = await startServerWithClient();
+    const result = await startServerWithClient();
+    servers.push(result);
+    const { server, ws } = result;
     await connectOk(ws);
 
     const id = "req-1";
@@ -50,13 +67,12 @@ describe("gateway config.apply", () => {
       // File may not exist if signal delivery is mocked, verify response was ok instead
       expect(res.ok).toBe(true);
     }
-
-    ws.close();
-    await server.close();
   });
 
   it("rejects invalid raw config", async () => {
-    const { server, ws } = await startServerWithClient();
+    const result = await startServerWithClient();
+    servers.push(result);
+    const { server, ws } = result;
     await connectOk(ws);
 
     const id = "req-2";
@@ -75,8 +91,5 @@ describe("gateway config.apply", () => {
       (o) => o.type === "res" && o.id === id,
     );
     expect(res.ok).toBe(false);
-
-    ws.close();
-    await server.close();
   });
 });