test(e2e): run chrome headless by default for local runs

Local wdio launched headed chrome on the WSLg desktop, so browser
windows popped up on the host display during every test run. Default to
headless (with --enable-unsafe-swiftshader, since chrome no longer
auto-falls back to software WebGL) and add a HEADED=1 escape hatch for
watching tests. CI behavior is unchanged.

Author: PaulHax

wdio.chrome.conf.ts

@@ -1,8 +1,10 @@
 import { config as sharedConfig, TEMP_DIR } from './wdio.shared.conf';
 
+const IS_CI = !!(process.env.CI || process.env.GITHUB_ACTIONS);
+
 // Chrome arguments for CI environments
 const chromeArgs: string[] = [];
-if (process.env.CI || process.env.GITHUB_ACTIONS) {
+if (IS_CI) {
   chromeArgs.push(
     '--no-sandbox',
     '--disable-dev-shm-usage',
@@ -11,6 +13,10 @@ if (process.env.CI || process.env.GITHUB_ACTIONS) {
   );
 }
 
+if (!IS_CI && !process.env.HEADED) {
+  chromeArgs.push('--headless=new', '--enable-unsafe-swiftshader');
+}
+
 export const config = {
   ...sharedConfig,
   capabilities: [