Consolidate domain exceptions into app.exceptions

Move all shared domain exception classes to backend/app/exceptions.py and update services/routers to import the canonical exceptions. Update docs to reflect the shared exceptions source.

backend/app/exceptions.py

@@ -51,3 +51,83 @@ class ConfigWriteError(Exception):
     def __init__(self, message: str) -> None:
         self.message = message
         super().__init__(message)
+
+
+class JailNameError(Exception):
+    """Raised when a jail name contains invalid characters."""
+
+
+class JailAlreadyActiveError(Exception):
+    """Raised when trying to activate a jail that is already active."""
+
+    def __init__(self, name: str) -> None:
+        self.name = name
+        super().__init__(f"Jail is already active: {name!r}")
+
+
+class JailAlreadyInactiveError(Exception):
+    """Raised when trying to deactivate a jail that is already inactive."""
+
+    def __init__(self, name: str) -> None:
+        self.name = name
+        super().__init__(f"Jail is already inactive: {name!r}")
+
+
+class FilterNotFoundError(Exception):
+    """Raised when the requested filter name is not found."""
+
+    def __init__(self, name: str) -> None:
+        self.name = name
+        super().__init__(f"Filter not found: {name!r}")
+
+
+class FilterAlreadyExistsError(Exception):
+    """Raised when trying to create a filter whose `.conf` or `.local` already exists."""
+
+    def __init__(self, name: str) -> None:
+        self.name = name
+        super().__init__(f"Filter already exists: {name!r}")
+
+
+class FilterNameError(Exception):
+    """Raised when a filter name contains invalid characters."""
+
+
+class FilterReadonlyError(Exception):
+    """Raised when trying to delete a shipped `.conf` filter with no `.local` override."""
+
+    def __init__(self, name: str) -> None:
+        self.name = name
+        super().__init__(
+            f"Filter {name!r} is a shipped default (.conf only); only user-created .local files can be deleted."
+        )
+
+
+class ActionNotFoundError(Exception):
+    """Raised when the requested action name is not found."""
+
+    def __init__(self, name: str) -> None:
+        self.name = name
+        super().__init__(f"Action not found: {name!r}")
+
+
+class ActionAlreadyExistsError(Exception):
+    """Raised when trying to create an action whose `.conf` or `.local` already exists."""
+
+    def __init__(self, name: str) -> None:
+        self.name = name
+        super().__init__(f"Action already exists: {name!r}")
+
+
+class ActionNameError(Exception):
+    """Raised when an action name contains invalid characters."""
+
+
+class ActionReadonlyError(Exception):
+    """Raised when trying to delete a shipped `.conf` action with no `.local` override."""
+
+    def __init__(self, name: str) -> None:
+        self.name = name
+        super().__init__(
+            f"Action {name!r} is a shipped default (.conf only); only user-created .local files can be deleted."
+        )