Remove Python app example and replace with header-echo server for testing

- Deleted the `/examples/docker/python-app` directory and associated files.
- Integrated a custom `header-echo` server for Kubernetes and Docker Compose tests.
- Updated Kubernetes and Docker Compose configurations to use the new `header-echo-server:test` image.
- Enhanced Kubernetes integration tests to validate JSON responses and Cloudflare IP translation behavior.

examples/fixtures/header-echo/Dockerfile

@@ -0,0 +1,11 @@
+FROM python:3.12-slim
+
+WORKDIR /app
+
+COPY server.py .
+
+RUN chmod +x server.py
+
+EXPOSE 8080
+
+CMD ["python3", "server.py"]

examples/fixtures/header-echo/README.md

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+# Header Echo Server - Test Fixture
+
+A lightweight Python HTTP server that echoes all request headers as JSON. Used for testing HAProxy plugins that manipulate headers and client IPs.
+
+## Purpose
+
+This test fixture is used by both Docker Compose and Kubernetes test suites to verify:
+- Header manipulation (e.g., X-Forwarded-For, CF-Connecting-IP)
+- IP restoration plugins (Cloudflare, custom CDN integrations)
+- Request routing and backend visibility
+
+## Usage
+
+### Docker Compose
+```yaml
+services:
+  webapp:
+    build: ../fixtures/header-echo
+    ports:
+      - "8080:8080"
+```
+
+### Kubernetes
+```bash
+# Build and load into kind cluster
+docker build -t header-echo-server:test .
+kind load docker-image header-echo-server:test --name your-cluster
+
+# Use in deployment
+spec:
+  containers:
+  - name: webapp
+    image: header-echo-server:test
+    imagePullPolicy: Never
+```
+
+### Manual Testing
+```bash
+# Start the server
+python3 server.py
+
+# Test it
+curl http://localhost:8080
+# Returns JSON with all headers, client IP, and X-Forwarded-For value
+```
+
+## Response Format
+
+```json
+{
+  "headers": {
+    "Host": "localhost:8080",
+    "User-Agent": "curl/7.81.0",
+    "Accept": "*/*"
+  },
+  "client_ip": "127.0.0.1",
+  "x_forwarded_for": "NOT SET"
+}
+```
+
+## Used By
+
+- `examples/docker/docker-compose-cloudflare.yml`
+- `examples/docker/test_docker_compose.py::TestCloudflare`
+- `examples/kubernetes/cloudflare.yml`
+- `examples/kubernetes/test_kubernetes.py::TestCloudflare`

examples/fixtures/header-echo/server.py

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+#!/usr/bin/env python3
+"""Simple HTTP server that echoes all request headers"""
+
+from http.server import HTTPServer, BaseHTTPRequestHandler
+import json
+
+class HeaderEchoHandler(BaseHTTPRequestHandler):
+    def do_GET(self):
+        self.send_response(200)
+        self.send_header('Content-Type', 'application/json')
+        self.end_headers()
+
+        # Collect all headers
+        headers = dict(self.headers)
+
+        # Add the client IP as seen by this server
+        response = {
+            'headers': headers,
+            'client_ip': self.client_address[0],
+            'x_forwarded_for': self.headers.get('X-Forwarded-For', 'NOT SET')
+        }
+
+        self.wfile.write(json.dumps(response, indent=2).encode())
+
+    def log_message(self, format, *args):
+        # Log to stdout
+        print(f"{self.address_string()} - {format % args}")
+
+if __name__ == '__main__':
+    port = 8080
+    server = HTTPServer(('0.0.0.0', port), HeaderEchoHandler)
+    print(f'Header echo server running on port {port}...')
+    server.serve_forever()