fix: resolve pylint and type-checking issues

- Fix return type annotation in SetupRedirectMiddleware.dispatch() to use Response instead of RedirectResponse
- Replace broad 'except Exception' with specific exception types (FileNotFoundError, ValueError, OSError, etc.)
- Rename AppConfig.validate() to validate_config() to avoid shadowing BaseModel.validate()
- Fix ValidationResult.errors field to use List[str] with default_factory
- Add pylint disable comments for intentional broad exception catches during shutdown
- Rename lifespan parameter to _application to indicate unused variable
- Update all callers to use new validate_config() method name

src/server/middleware/setup_redirect.py

@@ -11,7 +11,7 @@ from typing import Callable
 
 from fastapi import Request
 from starlette.middleware.base import BaseHTTPMiddleware
-from starlette.responses import RedirectResponse
+from starlette.responses import RedirectResponse, Response
 from starlette.types import ASGIApp
 
 from src.server.services.auth_service import auth_service
@@ -91,11 +91,11 @@ class SetupRedirectMiddleware(BaseHTTPMiddleware):
             config = config_service.load_config()
             
             # Validate the loaded config
-            validation = config.validate()
+            validation = config.validate_config()
             if not validation.valid:
                 return True
                 
-        except Exception:
+        except (FileNotFoundError, ValueError, OSError, AttributeError):
             # If we can't load or validate config, setup is needed
             return True
         
@@ -103,7 +103,7 @@ class SetupRedirectMiddleware(BaseHTTPMiddleware):
     
     async def dispatch(
         self, request: Request, call_next: Callable
-    ) -> RedirectResponse:
+    ) -> Response:
         """Process the request and redirect to setup if needed.
         
         Args: