Make action response and error non-optional

Updated ActionResponse type to make `response` and `error` fields mandatory but allowing null values. This change enforces more explicit handling of action outcomes and errors by avoiding optionality and using null to indicate absence.

These typings changes improve type safety and clarity of action results handling in the codebase.

Author: estib-vega

apps/desktop/src/lib/actions/types.ts

@@ -77,9 +77,9 @@ export class ButlerAction {
 	/** A GitBulter Oplog snapshot ID after the action was performed. */
 	snapshotAfter!: string;
 	/** The outcome of the action, if it was successful. */
-	response?: Outcome;
+	response!: Outcome | null;
 	/** An error message if the action failed. */
-	error?: string;
+	error!: string | null;
 	/** The source of the action, if known. */
 	source!: ActionSource;
 }