docs: add K6 endpoints summary and quick start guide

- K6_ENDPOINTS_SUMMARY.md: Quick reference for all API endpoints with request/response shapes
- K6_QUICK_START.md: Practical guide with executable examples for search, auth, listing, and payment load tests
- Includes example K6 scripts, CI integration template, and troubleshooting
- Complete with load test scenarios and reporting options

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

playwright.config.ts

@@ -41,7 +41,7 @@ export default defineConfig({
       name: 'api',
       testDir: './e2e/api',
       use: {
-        baseURL: process.env.API_BASE_URL ?? 'http://localhost:3001',
+        baseURL: process.env.API_BASE_URL ?? 'http://localhost:3001/api/v1',
       },
     },
     // Web E2E tests — Chromium browser
@@ -58,7 +58,7 @@ export default defineConfig({
   webServer: [
     {
       command: 'pnpm --filter @goodgo/api run dev',
-      url: 'http://localhost:3001/api/docs',
+      url: 'http://localhost:3001/api/v1/docs',
       reuseExistingServer: !process.env.CI,
       timeout: 60_000,
       env: {