fix: replace broad except Exception with specific exception types

- jail_service: catch ValueError (fail2ban protocol error) instead of Exception
- health.py: catch AttributeError (not OSError/TypeError) for defensive checks
- ban_service: re-raise programming errors in geo lookup handlers
- server_service: catch Fail2BanConnectionError, Fail2BanProtocolError, ValueError
- config_writer: catch OSError instead of Exception

Programming errors now bubble to global handler instead of being silently caught.

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

backend/app/routers/health.py

@@ -84,7 +84,7 @@ async def health_check(
             components.append(
                 ComponentHealth(name="scheduler", healthy=False, message="Not initialised"),
             )
-    except Exception:  # pragma: no cover - defensive
+    except AttributeError:  # pragma: no cover - defensive
         scheduler_state = "unknown"
         components.append(
             ComponentHealth(name="scheduler", healthy=False, message="Not accessible"),
@@ -100,10 +100,11 @@ async def health_check(
             components.append(
                 ComponentHealth(name="cache", healthy=False, message="Not initialised"),
             )
-    except Exception:  # pragma: no cover - defensive
+    except AttributeError:  # pragma: no cover - defensive
         cache_state = "uninitialised"
-
-    # --- fail2ban ---
+        components.append(
+            ComponentHealth(name="cache", healthy=False, message="Not accessible"),
+        )
     fail2ban_online: bool = server_status.online
     if not fail2ban_online:
         components.append(