Let task agents create and manage subtasks

web/style.css

@@ -534,6 +534,14 @@ a.task-link {
   background: var(--accent-tint);
 }
 
+.task-list li.subtask a {
+  padding-left: calc(10px + 20px * (var(--depth) - 1));
+}
+
+.subtask-mark {
+  color: var(--muted);
+}
+
 .task-title {
   flex: 1;
   overflow: hidden;
@@ -1979,6 +1987,26 @@ pre.diff .mark {
   color: var(--muted);
 }
 
+.merge-targets {
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+  margin: 0 0 16px;
+}
+
+.merge-target {
+  display: flex;
+  align-items: baseline;
+  gap: 8px;
+  cursor: pointer;
+}
+
+.merge-target-hint {
+  display: block;
+  color: var(--muted);
+  font-size: 12px;
+}
+
 .merge-title {
   display: flex;
   align-items: center;