Feature: Full UI support for use_backend rules editing

✨ New Features:
- Added use_backend_rules validator to Frontend model
- UI now supports editing use_backend rules from Frontend Management page
- Array to string conversion for use_backend rules in edit modal

🔧 Model Improvements:
- Changed use_backend_rules field type from Optional[str] to Any (list support)
- Added parse_use_backend_rules validator (same logic as ACL/redirect rules)
- Handles 3 formats: Array, Textarea string (newline-separated), JSON string

💡 UI Improvements:
- Frontend edit modal automatically converts use_backend array to multi-line text
- Users can edit routing rules line by line in textarea
- Format: 'use_backend BackendName if condition'

✅ Complete Workflow:
1. Bulk Import: Config parsed → ACL + use_backend stored as array
2. Frontend Edit: Arrays converted to multi-line string in textarea
3. User edits ACL/use_backend rules in UI
4. Save: Textarea string → validator → array → database
5. Config Generation: Array → HAProxy config format

Example workflow:
  Parse: ['use_backend API if is_api']
  → Edit UI: 'use_backend API if is_api' (textarea)
  → User edits: 'use_backend API_v2 if is_api_v2'
  → Save: ['use_backend API_v2 if is_api_v2']
  → Generate: 'use_backend API_v2 if is_api_v2' (HAProxy config)

backend/models/frontend.py

@@ -20,7 +20,7 @@ class FrontendConfig(BaseModel):
     ssl_verify: Optional[str] = "optional"
     acl_rules: Any = []
     redirect_rules: Any = []
-    use_backend_rules: Optional[str] = None
+    use_backend_rules: Any = []  # Changed from Optional[str] to Any for list support
     request_headers: Optional[str] = None
     response_headers: Optional[str] = None
     tcp_request_rules: Optional[str] = None
@@ -72,6 +72,25 @@ class FrontendConfig(BaseModel):
             return v
         return []
     
+    @validator('use_backend_rules', pre=True, always=True)
+    def parse_use_backend_rules(cls, v):
+        if isinstance(v, str):
+            v = v.strip()
+            # Handle JSON string (e.g., "[]" or "[\"rule1\", \"rule2\"]")
+            if v.startswith('[') and v.endswith(']'):
+                try:
+                    parsed = json.loads(v)
+                    if isinstance(parsed, list):
+                        return parsed
+                except (json.JSONDecodeError, ValueError):
+                    pass
+            # Handle newline-separated string
+            if v:
+                return [rule.strip() for rule in v.split('\n') if rule.strip()]
+        elif isinstance(v, list):
+            return v
+        return []
+    
     # CRITICAL VALIDATION RULES FOR HAPROXY
     @validator('name')
     def validate_name(cls, v):

frontend/src/components/FrontendManagement.js

@@ -531,12 +531,19 @@ const FrontendManagement = () => {
       formattedRedirectRules = frontend.redirect_rules.join('\n');
     }
     
+    // Format use_backend rules for textarea (array to multi-line string)
+    let formattedUseBackendRules = frontend.use_backend_rules;
+    if (Array.isArray(frontend.use_backend_rules)) {
+      formattedUseBackendRules = frontend.use_backend_rules.join('\n');
+    }
+    
     form.setFieldsValue({
       ...frontend,
       ssl_enabled: frontend.ssl_enabled || false,
       ssl_certificate_ids: sslCertIds,
       acl_rules: formattedAclRules,
-      redirect_rules: formattedRedirectRules
+      redirect_rules: formattedRedirectRules,
+      use_backend_rules: formattedUseBackendRules
     });
     
     // Update SSL field visibility after setting values