feat(maestro): force-kill prompt in the web client

The kill button now sends the unforced DELETE immediately instead of
asking first. Only the daemon's guard refusal raises a prompt, and it is
a real dialog rather than confirm(), so it can offer the override the
daemon already implements.

The API error envelope is decoded into ApiRequestError, keeping the code
and the unsaved-work breakdown so the dialog names what is in the way.

web/src/types.ts

@@ -253,7 +253,12 @@ export type ClientControl =
   | { type: "Error"; code: string; message: string };
 
 export interface ApiError {
-  error: { code: string; message: string };
+  error: {
+    code: string;
+    message: string;
+    /** Set only by the kill guard (#79): what blocked the unforced kill. */
+    unsaved_work?: InTheWay;
+  };
 }
 
 export function sessionName(s: Session): string {