Extract canvas projection helpers and thin preview and node loading

docs/modernization/tasks.md

@@ -91,7 +91,7 @@ Status: In Progress
 
 Why now:
 `src/canvas.cpp` is still the biggest single architectural blocker at about
-2645 lines.
+2728 lines.
 
 Current slice:
 - Canvas state-management helpers for picking, clear/clear-all, layer
@@ -103,6 +103,11 @@ Current slice:
   `src/legacy_canvas_document_io_services.cpp` instead of staying inline in
   `src/canvas.cpp`, which materially reduces document IO ownership in the live
   render shell.
+- Canvas point-trace, unproject, project2D, face-to-shape, and camera
+  push/pop/get/set helpers now also live in
+  `src/legacy_canvas_projection_services.*` instead of staying inline in
+  `src/canvas.cpp`, which trims another coherent non-UI state/query pocket
+  from the live canvas shell.
 
 Write scope:
 - `src/canvas.cpp`
@@ -158,6 +163,11 @@ Current slice:
   `execute_stroke_draw_immediate_pass_sequence(...)` helper, which removes
   another live orchestration block from the node even though worker/readback
   flow still remains in the file.
+- `NodeStrokePreview` stroke preparation, dual-brush setup, and live-pass
+  request assembly now also route through retained preview execution helpers,
+  which trims another coherent setup pocket from
+  `src/node_stroke_preview.cpp` even though worker/readback ownership and
+  broader preview flow still remain inline.
 - `NodeCanvas` merged-path per-plane merged-texture draw execution now also
   routes through `execute_legacy_canvas_draw_merge_layer_texture(...)`.
 - `NodeCanvas` merged-path and non-blend checkerboard background setup now also
@@ -390,7 +400,7 @@ Status: In Progress
 
 Why now:
 `src/app_dialogs.cpp` still mixes document workflow decisions, export routing,
-dialog construction, and overlay ownership.
+dialog construction, and overlay ownership in one 168-line shell.
 
 Current slice:
 - Informational overlay opener paths for user manual, changelog, about,
@@ -439,7 +449,7 @@ Status: In Progress
 
 Why now:
 `src/app.cpp` still carries startup, frame flow, queue draining, recording,
-and composition logic in one 502-line file.
+and composition logic in one 575-line file.
 
 Current slice:
 - UI observer math now routes through `src/legacy_app_frame_services.cpp`
@@ -651,12 +661,19 @@ attached to it.
 
 #### ARC-UI-001 - Move Generic Node And Control Code Out Of `pp_legacy_ui_core`
 
-Status: Ready
+Status: In Progress
 
 Why now:
 `pp_ui_core` has layout, color, node lifetime, and overlay lifetime, but the
 generic widget layer still sits in `pp_legacy_ui_core`.
 
+Current slice:
+- `Node::load_internal(...)` child XML loading now routes through
+  `src/legacy_ui_node_loader.*` instead of staying inline in `src/node.cpp`.
+  That trims another coherent generic node-instantiation pocket and makes the
+  remaining scene-graph load path easier to isolate, even though ownership has
+  not yet moved into `pp_ui_core`.
+
 Write scope:
 - `src/node.cpp`
 - `src/layout.cpp`