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/styles.css

@@ -1058,6 +1058,64 @@ input.leaf-rename:focus {
   border-color: color-mix(in oklab, var(--danger) 40%, transparent);
 }
 
+/* ---------- forced-kill prompt (#81) ---------- */
+.kill-dialog {
+  position: fixed;
+  inset: 0;
+  z-index: var(--z-modal);
+  display: grid;
+  place-items: center;
+  padding: var(--sp-4);
+  background: oklch(0 0 0 / 0.5);
+  backdrop-filter: blur(4px);
+}
+
+.kill-dialog-panel {
+  width: min(400px, 100%);
+  padding: var(--sp-4);
+  background: var(--surface);
+  border: 1px solid var(--border-strong);
+  border-radius: var(--r-3);
+  box-shadow: var(--shadow-2);
+}
+
+.kill-dialog-title {
+  margin: 0 0 var(--sp-2);
+  font-family: var(--font-mono);
+  font-size: var(--fs-15);
+  color: var(--ink);
+}
+
+.kill-dialog-body {
+  margin: 0;
+  color: var(--muted);
+  font-size: var(--fs-13);
+  line-height: 1.5;
+}
+
+.kill-dialog-error {
+  margin: var(--sp-2) 0 0;
+  color: var(--danger);
+  font-size: var(--fs-13);
+}
+
+.kill-dialog-actions {
+  display: flex;
+  justify-content: flex-end;
+  gap: var(--sp-2);
+  margin-top: var(--sp-4);
+}
+
+.btn-danger {
+  color: var(--danger);
+  border-color: color-mix(in oklab, var(--danger) 40%, transparent);
+}
+
+.btn-danger:hover {
+  background: var(--danger-tint);
+  border-color: var(--danger);
+}
+
 /* ---------- empty / loading ---------- */
 
 .empty {