feat: Add authentication configuration and validation

- Introduced new authentication settings in config.py including `auth_enabled`, `admin_username`, `admin_password`, and `session_secret`.
- Added validation for `session_secret` to ensure it meets security requirements when authentication is enabled.
- Updated main.py to conditionally mount static files and log warnings if the directory is not found.
- Removed unused email template files and added new authentication and notification setup documentation.
- Implemented authentication configuration validation in validators.py and updated settings display.
- Enhanced the user interface with a new login template and SVG assets for branding.
- Added comprehensive guides for setting up authentication and notifications in the documentation.

app/utils/config_validator/__init__.py

@@ -6,6 +6,7 @@ from app.utils.config_validator.validators import (
     validate_email_config,
     validate_storage_configs,
     validate_notification_config,
+    validate_auth_config,
     check_all_configs
 )
 from app.utils.config_validator.masking import mask_sensitive_value
@@ -19,6 +20,7 @@ __all__ = [
     'validate_email_config',
     'validate_storage_configs',
     'validate_notification_config',
+    'validate_auth_config',
     'mask_sensitive_value',
     'get_provider_status',
     'get_settings_for_display',