Initial commit: Imperva WAF demo lab

Flight-booking app scaffolded from the source running on the GCP host,
plus the four-screen frontend and three OWASP attack endpoints (SQLi,
reflected XSS, path traversal) built and locally verified against a
live uvicorn/vite dev pair. Includes deploy.sh (local build -> ship
over ssh -> swap on host) and docs/ carried over from the handoff.

backend/requirements.txt

@@ -0,0 +1,3 @@
+fastapi==0.111.0
+uvicorn==0.30.1
+pydantic==2.7.4