feat(quality): Sprint 2 pre-deploy gates and server smoke tests

Extract Express app factory for testability, add Vitest/Supertest API
smoke tests, root npm run check script, and deployment docs. Fix
express-rate-limit IPv6 keyGenerator for feedback limiter.

Co-authored-by: Cursor <cursoragent@cursor.com>

server/vitest.config.ts

@@ -0,0 +1,14 @@
+import { defineConfig } from 'vitest/config'
+
+export default defineConfig({
+  test: {
+    environment: 'node',
+    include: ['src/**/*.test.ts'],
+    env: {
+      NODE_ENV: 'test',
+      SESSION_SECRET: 'test-session-secret-minimum-32-characters-long',
+      ORIGIN: 'http://localhost:5173',
+      RP_ID: 'localhost'
+    }
+  }
+})