Implement Phase 19 updates and user/editor verification

- Updated architectural specifications for Phase 19 scenery, backgrounds, and surface finishes to reflect implementation status and user verification results.
- Revised UI/UX specifications for background ground and wall color, plain background, and starter scene composition to indicate successful implementation and verification.
- Enhanced scenery controller and sandbox stage scripts to improve eraser functionality and user interactions.
- Adjusted test cases to align with the latest changes in scenery and background implementations, ensuring all checks pass successfully.
- Added new buttons for wall area erasure in the scenery capture bar and updated layout handling for better user experience.

docs/specs/phase_19_scenery_backgrounds_surface_finishes.md

@@ -1,6 +1,6 @@
 # Phase 19 — Scenery, backgrounds, and surface finishes: architecture and implementation specification
 
-> **Status:** Original Phase 19 scenery architecture and the approved Stage-relative sizing amendment are integrated; automated and render-capable checks pass. The camera-aware Sky architecture addendum below is specified for user sign-off and is not yet implemented. This specification follows the [accepted product brief](../plans/phase_19_scenery_backgrounds_surface_finishes.md), the [approved UI/UX specification](phase_19_scenery_backgrounds_ui_ux.md), and the [Stage panel UI system](stage_panel_ui_system.md). Full Phase 19 user/editor verification remains pending. The camera-aware Sky addendum supersedes the original static-detail statements in this document.
+> **Status (2026-10-22):** Phase 19 architecture is implemented and user/editor verified. The user completed the integrated visual and interaction checks; `tests/test_phase19_scenery.gd` passes **706 checks with 0 failures**. This specification follows the [verified product plan](../plans/phase_19_scenery_backgrounds_surface_finishes.md), the [UI/UX specification](phase_19_scenery_backgrounds_ui_ux.md), and the [Stage panel UI system](stage_panel_ui_system.md). The camera-aware Sky addendum supersedes the original static-detail statements below.
 
 ## Decisions and scope
 
@@ -241,7 +241,7 @@ Each row names a child path and a repeatable observation. Automated checks may c
 | Move a referenced `.prop` aside, reopen, repair selected missing artwork; cancel once then confirm | One neutral marker remains at saved position/depth, summary appears once, ordinary EDIT targets are not stolen, cancel keeps path/dirty state, and confirmed repair changes only that placement. Missing footprint/no-footprint group resize rules and PLAY marker presentation hold. Restore source and reopen to confirm live-reference visual update. |
 | Select each Sky, pan/zoom, PLAY/stop, reopen | The fixed gradient fills the screen without an edge or flicker; details follow the bounded response in the [Sky addendum](#phase-19-addition-camera-aware-sky-details). Foreground pixel colors are unchanged by Sky choice. Layer order remains Sky/wall/Far/Near/Ground/floor/actors through camera movement, simulation, and reload; ghosts/handles/capture bars disappear in PLAY. |
 
-Visual acceptance requires opening the affected scene in a render-capable Godot GUI, capturing the named chooser, normal/zoomed Stage, missing-art, group-preview, **Prop Editor sizing guide at Small/Big and narrow width, active single-piece handles/capture bar**, and PLAY states, and inspecting the pixels. Record capture location, scene/state, and observation. Interactive acceptance requires exercising the actual controls and input events, including RMB/Esc/touch cancellation, button sizing, grid-aligned move, commit on release, and a late release after cancellation. If GUI or input automation is unavailable after an attempted route, name the unverified outcomes and hand the user a focused reproducible check; a headless parse or screenshot file alone is insufficient. Phase 19 user/editor verification remains open until the child checks the integrated behavior.
+Visual acceptance requires opening the affected scene in a render-capable Godot GUI, capturing the named chooser, normal/zoomed Stage, missing-art, group-preview, **Prop Editor sizing guide at Small/Big and narrow width, active single-piece handles/capture bar**, and PLAY states, and inspecting the pixels. Record capture location, scene/state, and observation. Interactive acceptance requires exercising the actual controls and input events, including RMB/Esc/touch cancellation, button sizing, grid-aligned move, commit on release, and a late release after cancellation. If GUI or input automation is unavailable after an attempted route, name the unverified outcomes and hand the user a focused reproducible check; a headless parse or screenshot file alone is insufficient. **Closeout:** the user reports completing the Phase 19 editor verification on 2026-10-22; the automated scenery suite passes 706 checks. Plain Background save/reopen was also explicitly verified by the user.
 
 ## Trade-offs and future work