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>

package.json

@@ -7,6 +7,11 @@
     "translate:flyer": "node scripts/translate-flyer.mjs",
     "validate:i18n": "node scripts/validate-i18n-keys.mjs",
     "generate:flyer": "node scripts/generate-beta-flyer.mjs",
-    "generate:flyer:all": "node scripts/generate-beta-flyer.mjs --all"
+    "generate:flyer:all": "node scripts/generate-beta-flyer.mjs --all",
+    "lint": "npm run lint --prefix client",
+    "test": "npm run test --prefix client && npm run test --prefix server",
+    "build": "npm run build --prefix client && npm run build --prefix server",
+    "check": "bash scripts/predeploy-check.sh",
+    "predeploy": "npm run check"
   }
 }