feat(ui): multi-browser coverage for Playwright UI tests

Add firefox and webkit projects alongside chromium (desktop/mobile),
and enable reuseExistingServer so the fixture server isn't restarted
per run. Chromium/Firefox/WebKit browsers installed via
npx playwright install.

playwright.ui.config.ts

@@ -39,11 +39,11 @@ export default defineConfig({
 	},
 	projects: [
 		{
-			name: "desktop",
+			name: "desktop-chromium",
 			use: { browserName: "chromium", viewport: { width: 1280, height: 900 } },
 		},
 		{
-			name: "mobile",
+			name: "mobile-chromium",
 			use: {
 				browserName: "chromium",
 				viewport: { width: 390, height: 844 },
@@ -52,12 +52,20 @@ export default defineConfig({
 				hasTouch: true,
 			},
 		},
+		{
+			name: "desktop-firefox",
+			use: { browserName: "firefox", viewport: { width: 1280, height: 900 } },
+		},
+		{
+			name: "desktop-webkit",
+			use: { browserName: "webkit", viewport: { width: 1280, height: 900 } },
+		},
 	],
 	webServer: {
 		command: "node e2e/ui/fixture-server.mjs",
 		url: `${baseURL}/health`,
 		timeout: 60000,
-		reuseExistingServer: false,
+		reuseExistingServer: true,
 		env: { UI_TEST_PORT: String(port) },
 	},
 });