Merge pull request #1747 from schoeller/reference_only_entities

Reference-only entities (plugin API v9): a scene-scoped, in-memory
designation for plugin-owned display geometry, plus HostNotification
dispatch to native plugins so they can re-mark on DocumentOpened.

Resolves the new DeltaSnapshot site in block_editor.rs.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/scene/text/complex_lt.rs

@@ -382,6 +382,7 @@ pub fn apply_along(
             depth_override: None,
             display_visible: true,
             snap_only: false,
+            reference_only: false,
             plot_visible: true,
             fill_is_3d: false,
             fill_is_2d_solid: false,