Route layer merge through app core

docs/modernization/roadmap.md

@@ -501,6 +501,8 @@ rename, and merge-down labels/actions, and direct Layer menu commands now
 dispatch through `DocumentLayerMenuServices` before the legacy canvas/layer UI
 adapter continues execution. Layer menu clear now routes through the shared
 `DocumentCanvasClearServices` executor before the legacy canvas-clear adapter
+continues, and Layer menu merge now validates and dispatches through
+`DocumentLayerMergeServices` before the legacy layer-panel merge adapter
 continues.
 `pano_cli plan-animation-operation` exposes app-core planning for animation
 frame add, duplicate, remove, duration adjustment, timeline moves, timeline
@@ -1249,8 +1251,9 @@ Results:
   layer operation side-effect dispatch, no-op operation preservation,
   malformed operation rejection, Layer menu labels/actions, merge-down routing,
   animated merge blocking, missing selection handling, bad Layer menu state
-  rejection, Layer menu executor dispatch, and no-op menu execution
-  preservation.
+  rejection, Layer menu executor dispatch, no-op menu execution preservation,
+  merge-plan validation, unsupported animated merge rejection, merge executor
+  dispatch, and malformed merge-plan rejection.
 - `pano_cli_plan_layer_rename_smoke`,
   `pano_cli_plan_layer_rename_no_op_smoke`, and
   `pano_cli_plan_layer_rename_rejects_empty_name` passed and expose live
@@ -1261,6 +1264,9 @@ Results:
   `pano_cli_plan_layer_menu_missing_selection_smoke`, and
   `pano_cli_plan_layer_menu_rejects_bad_state` passed and expose live Layer
   menu planning as JSON automation.
+- `pano_cli_plan_layer_merge_smoke` and
+  `pano_cli_plan_layer_merge_animated_rejected` passed and expose live
+  merge execution planning as JSON automation.
 - `pano_cli_plan_layer_operation_add_smoke`,
   `pano_cli_plan_layer_operation_reorder_no_op_smoke`,
   `pano_cli_plan_layer_operation_highlight_smoke`, and