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_starter_scene_composition.md

@@ -1,6 +1,6 @@
 # Phase 19 — Starter Scene Composition: Architecture and Implementation Specification
 
-> **Status:** Implemented; focused behavior verification passed. Rendered-pixel and user/editor verification remain pending because the available Godot capture route exited before producing an image. The user requested an opaque Town Street Background ground layer and rows of ordinary-size walkable Ground tiles in both starters instead of oversized terrain blocks.
+> **Status (2026-10-22):** Implemented and user/editor verified. The user verified the Town Street and Living Room compositions in the editor. The Phase 19 scenery suite passes **706 checks with 0 failures**; see the [Phase 19 handoff](../plans/phase_19_handoff.md). The user-requested opaque Town Street Background ground layer and ordinary-size walkable Ground tiles are included.
 >
 > **Approvals:** Everyday Storybook direction approved; architecture defaults approved: **1,280×720 logical-pixel reference viewport (16:9)**, saved zoom **0.5**, horizontal pan guarantee **±1,000 world units**, and **100 world units** of end margin.
 >
@@ -140,13 +140,13 @@ Phase 2 must inspect rendered captures from a render-capable Godot Stage at open
 - The initial pass promoted both snapshots to v1.6 and aligned visible bases, but used oversized scaled walkable blocks and omitted Town Background ground. The user identified those issues; that surface implementation was superseded by the tile/backdrop revision below.
 - `StageStarterCardPreview` now derives a square crop from the saved camera position and zoom. At zoom 0.5, it frames a 1,440 × 1,440 world-unit opening crop in the existing 220 × 220 usable preview area.
 - `/Applications/Godot.app/Contents/MacOS/Godot --path /Users/ryan/Projects/stickman --headless --rendering-method gl_compatibility --script res://tests/test_phase19_starter_scene_composition.gd` passed **515 assertions** on Godot 4.7.1. It covers production scene loading, save/reopen, surface bounds, window opening, preview transforms, base contacts, PLAY support, navigation across each tile row, and sidewalk-to-road access. Town Asphalt has 27 scale-1 tiles spanning 5,184 units; a PLAY actor moved from x=2,280 to x=2,500 and landed grounded on the road at feet y=15.31. The navigation query from center to the opposite walk line follows the exposed right curb through `(2400, -4)` and `(2400, 12)`. Measured contact gaps at the saved zoom were 0.0 logical px for Town artwork; 0.0–0.123 px for Living Room floor artwork; and 0.025–0.225 px for the three Props. These are production-loaded geometry measurements, not pixel samples from rendered captures.
-- `/Applications/Godot.app/Contents/MacOS/Godot --path /Users/ryan/Projects/stickman --headless --rendering-method gl_compatibility --script res://tests/test_phase19_scenery.gd` exits 1. The Town/Living starter surface, count, scale, bounds, seam, pan-margin, and camera assertions pass; the nine remaining failures concern the Sky/surface preview card count, a wall-erasure document-change signal, and Edit Scenery erase/Cancel capture-bar behavior. These same failures were present before the latest tile and curb changes. The environment also reports a Stage autosave warning during that run.
+- An earlier Phase 19 scenery-suite run exited 1 with nine failures in Sky/surface previews and Edit Scenery eraser/capture-bar behavior. This historical result was superseded by the 2026-10-22 retest: **706 checks passed, 0 failed**.
 - Rendered-pixel inspection could not be completed here: a bounded GUI capture attempt exited 134 without output or an image, and an earlier headless compatibility capture produced no image before it was stopped after 30 seconds. The default headless Vulkan test path also crashed in shader translation. The focused compatibility test exited successfully; the environment printed a macOS CA-certificate lookup warning.
-- Remaining user/editor checks: opening frames, ±1,000 camera pan endpoints, the Town background and tile appearance, both starter cards, a narrower viewport, dramatic zoom-in, and rendered seams/Sky inspection. User-supplied Town Street imagery exposed the missing background; this revised pass still needs a fresh rendered visual review. Automated geometry and PLAY checks cover support across tile seams and the curb step.
+- User/editor checks listed here are complete as of 2026-10-22. The user verified the starter compositions and the remaining Phase 19 visual/interaction scenarios; see the [Phase 19 handoff](../plans/phase_19_handoff.md) for the consolidated record.
 
 ### User visual follow-up (2026-10-21)
 
-The user's Town Street capture showed Sky clouds visible below the skyline because the initial implementation omitted Background ground. The user also rejected the oversized scaled TerrainBlocks used for walkable surfaces and requested left-to-right rows of ordinary Ground tiles in both templates. The current revision adds opaque non-walkable Grass Background ground behind Town Street and uses adjacent scale-1 tiles for Sidewalk, Asphalt, and Living Room Wood. Sidewalk uses 25 tiles; Asphalt uses 27, extending one tile beyond each sidewalk end so the road is physically reachable. The focused production-path test passed 515 assertions, including seam routing and a grounded PLAY step onto Asphalt. Fresh rendered review and user/editor checks remain pending.
+The user's Town Street capture showed Sky clouds visible below the skyline because the initial implementation omitted Background ground. The user also rejected the oversized scaled TerrainBlocks used for walkable surfaces and requested left-to-right rows of ordinary Ground tiles in both templates. The current revision adds opaque non-walkable Grass Background ground behind Town Street and uses adjacent scale-1 tiles for Sidewalk, Asphalt, and Living Room Wood. Sidewalk uses 25 tiles; Asphalt uses 27, extending one tile beyond each sidewalk end so the road is physically reachable. The focused production-path test passed 515 assertions, including seam routing and a grounded PLAY drop onto Asphalt. The final user/editor verification and 706-check Phase 19 suite result supersede this earlier pending status.
 
 ## Trade-offs and deferred work