cleanup: remove old unused tooling and reference configs

Remove:
- @lhci/cli + lighthouserc.cjs (Lighthouse CI, never used in CI pipeline)
- @playwright/test + e2e/ tests + playwright.config.ts (E2E tests not used)
- setup/ directory (emulator/nitro reference install configs)
- Build artifacts: .next.prev/, coverage/, backups/

playwright.config.ts

@@ -1,33 +0,0 @@
-import { defineConfig, devices } from "@playwright/test";
-
-export default defineConfig({
-	testDir: "./e2e",
-	fullyParallel: true,
-	forbidOnly: !!process.env.CI,
-	retries: process.env.CI ? 2 : 0,
-	workers: process.env.CI ? 1 : undefined,
-	reporter: "html",
-	use: {
-		baseURL: process.env.NEXT_PUBLIC_APP_URL || "http://localhost:3000",
-		trace: "on-first-retry",
-	},
-	projects: [
-		{
-			name: "chromium",
-			use: { ...devices["Desktop Chrome"] },
-		},
-		{
-			name: "firefox",
-			use: { ...devices["Desktop Firefox"] },
-		},
-		{
-			name: "webkit",
-			use: { ...devices["Desktop Safari"] },
-		},
-	],
-	webServer: {
-		command: "pnpm dev",
-		url: "http://localhost:3000",
-		reuseExistingServer: !process.env.CI,
-	},
-});