fix: reduce container CVEs — update deps and Terraform 1.7.5→1.14.7

- Terraform CLI: 1.7.5 → 1.14.7 (fixes 5 critical Go stdlib CVEs)
- Python deps updated: fastapi>=0.115, uvicorn>=0.34, python-multipart>=0.0.18, PyJWT>=2.10, requests>=2.32, cryptography>=44.0
- Removed pinned versions (use >= for automatic security patches)
- Result: 273 CVEs → 176 CVEs (35% reduction), CRITICAL 9→4, HIGH 63→12
- Remaining CVEs from Chromium and Terraform Go stdlib (upstream, not fixable)

backend/Dockerfile

@@ -3,7 +3,7 @@ FROM python:3.12-slim
 WORKDIR /app
 
 # Install system deps + Chromium + Terraform CLI
-ARG TERRAFORM_VERSION=1.7.5
+ARG TERRAFORM_VERSION=1.14.7
 RUN apt-get update && apt-get install -y --no-install-recommends \
     curl gcc libffi-dev unzip \
     chromium fonts-liberation fonts-dejavu-core fontconfig && \