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/config.py

@@ -37,11 +37,17 @@ class Settings(BaseSettings):
     gotenberg_url: str
     external_hostname: str = "localhost"  # Default to localhost
 
+    # Authentication settings
+    auth_enabled: bool = True  # Default to enabled
+    admin_username: Optional[str] = None
+    admin_password: Optional[str] = None
+    session_secret: Optional[str] = None
+
     # Authentik
     authentik_client_id: Optional[str] = None
     authentik_client_secret: Optional[str] = None
     authentik_config_url: Optional[str] = None
-    auth_enabled: bool = True  # Default to enabled
+    oauth_provider_name: Optional[str] = None  # Name to display for the OAuth provider
 
     # IMAP 1
     imap1_host: Optional[str] = None
@@ -162,6 +168,15 @@ class Settings(BaseSettings):
             return []
         return v
 
+    @validator('session_secret')
+    def validate_session_secret(cls, v, values):
+        """Validate that session_secret is set and has sufficient length when auth is enabled"""
+        if values.get('auth_enabled') and not v:
+            raise ValueError("SESSION_SECRET must be set when AUTH_ENABLED=True")
+        if values.get('auth_enabled') and v and len(v) < 32:
+            raise ValueError("SESSION_SECRET must be at least 32 characters long")
+        return v
+
     # Get build date from environment or file
     @property
     def build_date(self) -> str: