test: add Playwright E2E infrastructure with smoke test

Set up Playwright with Chromium, dev server auto-start, test helpers
for seeding bots and programmatic auth. Added smoke spec that verifies
homepage and leaderboard load without crashes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

e2e/helpers/auth.ts

@@ -0,0 +1,37 @@
+/**
+ * E2E authentication helpers.
+ * Provides programmatic login for tests without browser extension interaction.
+ */
+
+import { randomPubkey } from './setup.js'
+
+/**
+ * Create a test identity (pubkey + nsec equivalent).
+ * For E2E tests, we use direct pubkey-based login (legacy endpoint)
+ * since we can't interact with NIP-07 browser extensions.
+ */
+export function createTestIdentity() {
+  return {
+    pubkey: randomPubkey(),
+    // In a real NIP-98 flow, this would be a signed event
+    // For testing, we use the legacy login endpoint
+  }
+}
+
+/**
+ * Login via legacy endpoint and get bot data.
+ * Returns bot info if the pubkey has a registered bot.
+ */
+export async function loginWithPubkey(baseURL: string, pubkey: string): Promise<{ bot?: { id: string; name: string } }> {
+  const res = await fetch(`${baseURL}/api/auth/login`, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ pubkey }),
+  })
+
+  if (!res.ok) {
+    return {}
+  }
+
+  return res.json()
+}