Move config file exceptions into app.exceptions

Move ConfigDirError, ConfigFileNotFoundError, ConfigFileExistsError, ConfigFileWriteError, and ConfigFileNameError from raw_config_io_service into the shared domain exception module. Update router and tests to import the exceptions from app.exceptions.

Docs/Refactoring.md

@@ -7,4 +7,5 @@ This document catalogues architecture violations, code smells, and structural is
 ## Completed Refactors
 
 - Moved `Fail2BanConnectionError` and `Fail2BanProtocolError` from `backend/app/utils/fail2ban_client.py` into `backend/app/exceptions.py`. Updated all router, service, and test call sites to import these domain exceptions from `app.exceptions` and retained backward compatibility through re-exporting in `app.utils.fail2ban_client`.
+- Moved config file exceptions (`ConfigDirError`, `ConfigFileNotFoundError`, `ConfigFileExistsError`, `ConfigFileWriteError`, `ConfigFileNameError`) from `backend/app/services/raw_config_io_service.py` into `backend/app/exceptions.py`. Updated router and tests to import the shared domain exceptions from `app.exceptions`.
 

Docs/Tasks.md

@@ -44,6 +44,8 @@ Reference: `Docs/Refactoring.md` for full analysis of each issue.
 
 **Why this is needed:** Routers should not reach into service internals to import exception types. All domain exceptions belong in the central registry so `main.py` global handlers and any future middleware can catch them uniformly.
 
+**Status:** Completed ✅
+
 ---
 
 ### Task 3 — Eliminate the `config_file_service.py` delegation façade