Add Playwright accessibility and mobile layout e2e tests

Set up end-to-end test infrastructure with Docker Compose test
environment, Playwright config, and automated global setup/teardown
that seeds a test database and creates fixtures via the API.

Tests cover 11 pages across both dark/light themes for WCAG 2.0 AA
accessibility (axe-core), and across 3 viewports (mobile, tablet,
desktop) for horizontal overflow and touch target validation.

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

frontend/e2e/fixtures.ts

@@ -0,0 +1,17 @@
+import { readFileSync } from 'node:fs'
+import { resolve } from 'node:path'
+
+interface Fixtures {
+  gameId: number
+  runId: number
+  genlockeId: number
+}
+
+let cached: Fixtures | null = null
+
+export function loadFixtures(): Fixtures {
+  if (cached) return cached
+  const raw = readFileSync(resolve(__dirname, '.fixtures.json'), 'utf-8')
+  cached = JSON.parse(raw) as Fixtures
+  return cached
+}