Add comprehensive documentation for DMARQ, including user guides, deployment instructions, and feature descriptions

- Created main documentation index and user guide with sections on getting started, dashboard overview, managing domains, and reports.
- Added detailed deployment guide for Docker and manual installation.
- Included user-friendly explanations of DMARC, its benefits, and how to manage domains and reports.
- Implemented visual assets for dashboard, domains, IMAP, and reports.
- Established requirements for documentation build using MkDocs and Material theme.
- Integrated navigation structure for easy access to all documentation sections.

backend/app/utils/domain_validator.py

@@ -0,0 +1,70 @@
+import re
+import socket
+from typing import Dict, Tuple, Union, Optional
+
+
+def validate_domain(domain_name: str) -> Tuple[bool, Optional[str]]:
+    """
+    Validates a domain name for format and resolvability.
+    
+    Args:
+        domain_name: The domain name to validate
+        
+    Returns:
+        Tuple containing (is_valid, error_message)
+        - is_valid: Boolean indicating if domain is valid
+        - error_message: String with error message if not valid, None if valid
+    """
+    # Check for empty domain
+    if not domain_name:
+        return False, "Domain name cannot be empty"
+    
+    # Check domain format with regex
+    # This regex allows domain names with alphanumeric characters, hyphens,
+    # and periods as separators. It enforces proper domain structure.
+    domain_pattern = r'^(?:[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?\.)+[a-zA-Z0-9][a-zA-Z0-9-]{0,61}[a-zA-Z0-9]$'
+    if not re.match(domain_pattern, domain_name):
+        return False, "Invalid domain format"
+    
+    # Check if domain exists by attempting to resolve DNS
+    try:
+        socket.gethostbyname(domain_name)
+        return True, None
+    except socket.gaierror:
+        # We could consider this valid if we don't require DNS resolution,
+        # but since DMARC requires valid DNS, we'll mark it as warning
+        return False, "Domain could not be resolved (DNS lookup failed)"
+
+
+def validate_domain_config(domain_data: Dict) -> Dict[str, Union[bool, str]]:
+    """
+    Validates domain configuration data for creating or updating domains.
+    
+    Args:
+        domain_data: Dictionary with domain configuration
+        
+    Returns:
+        Dictionary with validation results containing:
+        - valid: Boolean indicating if configuration is valid
+        - errors: Dict of field-specific errors
+    """
+    errors = {}
+    
+    # Validate domain name
+    if "name" in domain_data:
+        is_valid, error_msg = validate_domain(domain_data["name"])
+        if not is_valid:
+            errors["name"] = error_msg
+    else:
+        errors["name"] = "Domain name is required"
+    
+    # Validate description (optional but with max length)
+    if "description" in domain_data and domain_data["description"]:
+        if len(domain_data["description"]) > 255:
+            errors["description"] = "Description is too long (max 255 characters)"
+    
+    # Return validation results
+    return {
+        "valid": len(errors) == 0,
+        "errors": errors
+    }