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>

docker-compose.test.yml

@@ -0,0 +1,36 @@
+services:
+  test-db:
+    image: postgres:16-alpine
+    ports:
+      - "5433:5432"
+    environment:
+      - POSTGRES_USER=postgres
+      - POSTGRES_PASSWORD=postgres
+      - POSTGRES_DB=nuzlocke_test
+    tmpfs:
+      - /var/lib/postgresql/data
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U postgres"]
+      interval: 2s
+      timeout: 5s
+      retries: 10
+    restart: "no"
+
+  test-api:
+    build:
+      context: ./backend
+      dockerfile: Dockerfile
+    ports:
+      - "8000:8000"
+    environment:
+      - DATABASE_URL=postgresql+asyncpg://postgres:postgres@test-db:5432/nuzlocke_test
+      - DEBUG=true
+    depends_on:
+      test-db:
+        condition: service_healthy
+    healthcheck:
+      test: ["CMD-SHELL", "curl -f http://localhost:8000/ || exit 1"]
+      interval: 3s
+      timeout: 5s
+      retries: 15
+    restart: "no"