feat(kanban): drag-to-delete trash zone + bulk delete for task cards

Salvages #28125 by @Jpalmer95. Adds:
- Drag-to-delete trash zone in the kanban dashboard
- Bulk delete endpoint with cascading delete_task cleanup
- Frontend updates (drag visual + drop handler)
- Confirmation prompt before delete

Resolved end-of-file test conflict by appending both halves.

tests/hermes_cli/test_kanban_db.py

@@ -816,6 +816,34 @@ def test_list_tasks_order_by(kanban_home):
         except ValueError as e:
             assert "order_by must be one of" in str(e)
 
+def test_delete_task_removes_task_and_cascades(kanban_home):
+    with kb.connect() as conn:
+        t = kb.create_task(conn, title="to-delete", assignee="alice")
+        kb.add_comment(conn, t, "user", "comment")
+        kb.add_comment(conn, t, "user", "another")
+        assert kb.delete_task(conn, t)
+        assert kb.get_task(conn, t) is None
+        assert len(kb.list_comments(conn, t)) == 0
+        assert len(kb.list_events(conn, t)) == 0
+        assert len(kb.list_runs(conn, t)) == 0
+
+
+def test_delete_task_returns_false_for_missing_task(kanban_home):
+    with kb.connect() as conn:
+        assert not kb.delete_task(conn, "t_nonexistent")
+
+
+def test_delete_task_cascades_links(kanban_home):
+    with kb.connect() as conn:
+        p = kb.create_task(conn, title="parent")
+        c = kb.create_task(conn, title="child", parents=[p])
+        child = kb.get_task(conn, c)
+        assert child is not None and child.status == "todo"
+        kb.delete_task(conn, p)
+        assert kb.get_task(conn, p) is None
+        child_after = kb.get_task(conn, c)
+        assert child_after is not None and child_after.status == "ready"
+
 
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