refactor: Extract fail2ban response utilities into shared module

Consolidate duplicate _ok(), _to_dict(), ensure_list(), and is_not_found_error()
functions from 6 service modules into a single canonical implementation at
backend/app/utils/fail2ban_response.py.

Changes:
- Create fail2ban_response.py with canonical implementations
- Remove local duplicates from: ban_service, jail_service, config_service,
  health_service, server_service, config_file_utils
- Update all imports to use shared module
- Add comprehensive docstrings and examples
- Update Architecture.md and Backend-Development.md documentation

Benefits:
- Single source of truth for response parsing logic
- Eliminates code duplication across service layer
- Improves maintainability and consistency
- Enables centralized bug fixes and improvements

Tests: All 228 service tests passing, no regressions

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/app/utils/config_file_utils.py

@@ -17,19 +17,18 @@ from app.exceptions import (
     JailNameError,
 )
 from app.models.config import (
-    ActionConfig,
     BantimeEscalation,
     InactiveJail,
     JailValidationIssue,
     JailValidationResult,
 )
-from app.utils import conffile_parser
 from app.utils.constants import FAIL2BAN_TRUTHY_VALUES
 from app.utils.fail2ban_client import (
     Fail2BanClient,
     Fail2BanConnectionError,
     Fail2BanResponse,
 )
+from app.utils.fail2ban_response import ok, to_dict
 
 log: structlog.stdlib.BoundLogger = structlog.get_logger()
 
@@ -256,26 +255,8 @@ async def _get_active_jail_names(socket_path: str) -> set[str]:
     try:
         client = Fail2BanClient(socket_path=socket_path, timeout=_SOCKET_TIMEOUT)
 
-        def _to_dict_inner(pairs: object) -> dict[str, object]:
-            if not isinstance(pairs, (list, tuple)):
-                return {}
-            result: dict[str, object] = {}
-            for item in pairs:
-                try:
-                    k, v = item
-                    result[str(k)] = v
-                except (TypeError, ValueError):
-                    pass
-            return result
-
-        def _ok(response: object) -> object:
-            code, data = cast("Fail2BanResponse", response)
-            if code != 0:
-                raise ValueError(f"fail2ban error {code}: {data!r}")
-            return data
-
-        status_raw = _ok(await client.send(["status"]))
-        status_dict = _to_dict_inner(status_raw)
+        status_raw = ok(await client.send(["status"]))
+        status_dict = to_dict(status_raw)
         jail_list_raw: str = str(status_dict.get("Jail list", "") or "").strip()
         if not jail_list_raw:
             return set()