chore(dev-server-legacy): add comment about future src import rewrite

Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bennypowers

packages/dev-server-legacy/test/transform-html.test.ts

@@ -3,6 +3,7 @@ import assert from 'node:assert/strict';
 import { createTestServer } from '@web/dev-server-core/test-helpers';
 import { fetchText, expectIncludes } from '@web/dev-server-core/test-helpers';
 
+// rewrite to ../src/legacyPlugin.ts when TS 5.7+ / rewriteRelativeImportExtensions
 import { legacyPlugin } from '../dist/legacyPlugin.js';
 import { modernUserAgents, legacyUserAgents } from './userAgents.ts';
 

packages/dev-server-legacy/test/transform-js.test.ts

@@ -3,6 +3,7 @@ import assert from 'node:assert/strict';
 import { createTestServer } from '@web/dev-server-core/test-helpers';
 import { fetchText, expectIncludes, expectNotIncludes } from '@web/dev-server-core/test-helpers';
 
+// rewrite to ../src/legacyPlugin.ts when TS 5.7+ / rewriteRelativeImportExtensions
 import { legacyPlugin } from '../dist/legacyPlugin.js';
 import { modernUserAgents, legacyUserAgents } from './userAgents.ts';