fix(backend): install curl for Docker healthchecks

The backend container was marked as unhealthy because the healthcheck
command uses curl but curl wasn't installed in the python:3.11-slim image.

- Added apt-get install curl to Dockerfile
- This fixes the healthcheck failures in production
- Container was actually running fine, just couldn't report health status

Author: SkySingh04

backend/Dockerfile

@@ -2,6 +2,9 @@ FROM python:3.11-slim
 
 WORKDIR /app
 
+# Install curl for healthchecks
+RUN apt-get update && apt-get install -y curl && rm -rf /var/lib/apt/lists/*
+
 # Install backend runtime deps
 COPY backend/requirements.txt /app/requirements.txt
 RUN pip install --no-cache-dir -r /app/requirements.txt