test: build every in-process WebServer on port 0 (#440)

The files on the guard's legacy list build new WebServer(0, …) and read server.boundPort after start(), as sse-tile-grid-filter does. Files with several servers read each server's own port; quick-start's local helper lost its port parameter so the literal 0 sits where the server is built. Header comments that named a port say "ephemeral". No assertion changed except where it embedded the port.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

test/static-cache-headers.test.ts

@@ -22,8 +22,6 @@ import { afterAll, beforeAll, describe, expect, it } from 'vitest';
 
 import { WebServer } from '../src/web/server.js';
 
-const TEST_PORT = 3183;
-
 /**
  * Fetch and fully drain the body. Both halves matter for teardown: an unconsumed
  * body leaves undici holding the socket, and a pooled keep-alive socket makes
@@ -40,9 +38,9 @@ describe('static asset Cache-Control headers', () => {
   let baseUrl: string;
 
   beforeAll(async () => {
-    server = new WebServer(TEST_PORT, false, true);
+    server = new WebServer(0, false, true);
     await server.start();
-    baseUrl = `http://localhost:${TEST_PORT}`;
+    baseUrl = `http://localhost:${server.boundPort}`;
   });
 
   afterAll(async () => {