Extract fill modes, preview runtime pockets, and brush item UI

docs/modernization/tasks.md

@@ -132,6 +132,10 @@ Current slice:
   `src/legacy_canvas_mode_transform.cpp` instead of staying inline in
   `src/canvas_modes.cpp`, which materially thins another retained
   transform-mode pocket from the broader canvas/render hotspot family.
+- The `CanvasModeFill` and `CanvasModeFloodFill` interaction families now
+  also live in `src/legacy_canvas_mode_fill.cpp` instead of staying inline in
+  `src/canvas_modes.cpp`, which materially thins another retained fill-mode
+  pocket from the live canvas-mode shell.
 - The live `Canvas::stroke_draw()` orchestration now also lives in
   `src/legacy_canvas_stroke_live_services.cpp` instead of staying inline in
   `src/canvas.cpp`, which materially thins another large retained live
@@ -231,6 +235,9 @@ Current slice:
   which trims another coherent setup pocket from
   `src/node_stroke_preview.cpp` even though worker/readback ownership and
   broader preview flow still remain inline.
+- `src/node_stroke_preview.cpp` is now 280 lines after moving the preview
+  background-capture and stroke-frame planning pocket into
+  `legacy_node_stroke_preview_runtime_services.*`.
 - The remaining immediate preview pass shell in
   `NodeStrokePreview::draw_stroke_immediate()` now also routes through
   `execute_legacy_node_stroke_preview_draw_immediate_shell(...)`, which
@@ -1133,6 +1140,11 @@ Current slice:
   `src/node_panel_brush.cpp`, which trims a coherent retained brush-workflow
   pocket from the live UI node even though cloud and package-worker ownership
   still remain separate follow-up work.
+- `NodeButtonBrush` clone/init/icon/read/write/draw behavior and
+  `NodeBrushPresetItem` clone/init/draw behavior now also live in
+  `src/legacy_brush_panel_item_ui.*` instead of staying inline in
+  `src/node_panel_brush.cpp`, which trims the remaining brush-item UI pocket
+  from the live brush panel file.
 - `NodePanelBrushPreset` save/restore plus PPBR/ABR import/export routing now
   also lives in `src/legacy_brush_preset_services.*` instead of staying inline
   in `src/node_panel_brush.cpp`, which trims another large preset-workflow