feat(monitoring): add Redis exporter + Sentry docs to deployment guide

- Add redis-exporter container to docker-compose (oliver006/redis_exporter, 32MB)
- Add Redis scrape target to Prometheus config
- Add 4 Redis alert rules: RedisDown, HighMemory, HighConnections, RejectedConnections
- Document Step 19b (Sentry Error Tracking) in Hetzner deployment guide
- Document Step 19c (Redis Monitoring) in Hetzner deployment guide
- Update resource budget and port reference tables

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/guides/user-management.md

@@ -134,8 +134,8 @@ if __name__ == "__main__":
 curl -X POST "http://localhost:8000/register" \
      -H "Content-Type: application/json" \
      -d '{
-       "email": "user@example.com", 
-       "username": "newuser", 
+       "email": "user@example.com",
+       "username": "newuser",
        "password": "password123"
      }'
 ```
@@ -158,7 +158,7 @@ curl -X POST "http://localhost:8000/register" \
 curl -X POST "http://localhost:8000/login" \
      -H "Content-Type: application/json" \
      -d '{
-       "username": "admin", 
+       "username": "admin",
        "password": "admin123"
      }'
 ```
@@ -202,8 +202,8 @@ curl -X POST "http://localhost:8000/products" \
      -H "Authorization: Bearer YOUR_JWT_TOKEN_HERE" \
      -H "Content-Type: application/json" \
      -d '{
-       "marketplace_product_id": "TEST001", 
-       "title": "Test MarketplaceProduct", 
+       "marketplace_product_id": "TEST001",
+       "title": "Test MarketplaceProduct",
        "description": "A test product for demonstration",
        "price": "19.99",
        "brand": "Test Brand",
@@ -267,13 +267,13 @@ Authorization: Bearer <your_jwt_token>
 def safe_api_call(token, endpoint, method="GET", data=None):
     """Make API call with proper error handling"""
     headers = {"Authorization": f"Bearer {token}"}
-    
+
     try:
         if method == "GET":
             response = requests.get(f"{BASE_URL}{endpoint}", headers=headers)
         elif method == "POST":
             response = requests.post(f"{BASE_URL}{endpoint}", json=data, headers=headers)
-        
+
         if response.status_code == 401:
             print("Authentication failed - token may be expired")
             return None
@@ -285,7 +285,7 @@ def safe_api_call(token, endpoint, method="GET", data=None):
         else:
             print(f"API call failed: {response.status_code} - {response.text}")
             return None
-            
+
     except requests.exceptions.RequestException as e:
         print(f"Request failed: {e}")
         return None
@@ -340,7 +340,7 @@ class APIClient {
             headers: {'Content-Type': 'application/json'},
             body: JSON.stringify({username, password})
         });
-        
+
         if (response.ok) {
             const data = await response.json();
             this.token = data.access_token;
@@ -361,17 +361,17 @@ class APIClient {
         if (data) config.body = JSON.stringify(data);
 
         const response = await fetch(`${this.baseURL}${endpoint}`, config);
-        
+
         if (response.status === 401) {
             // Token expired, redirect to login
             localStorage.removeItem('jwt_token');
             window.location.href = '/login';
             return;
         }
-        
+
         return response.json();
     }
 }
 ```
 
-This authentication system provides secure access control for all API endpoints while maintaining ease of use for developers integrating with the system.
+This authentication system provides secure access control for all API endpoints while maintaining ease of use for developers integrating with the system.