Add tests for scenery surface caching and preview behavior

- Introduced `test_scenery_brick_preview.gd` to validate focused placement and CPU draw-cost for large brick walls.
- Added `test_scenery_surface_cache.gd` to assess texture budget, visual equivalence, and cache invalidation.
- Created `test_scenery_surface_preview.gd` to evaluate adaptive preview selection and placement behavior.
- Implemented various helper functions to measure drawing performance and validate expected behaviors during tests.
- Added unique identifiers for new test files to ensure proper tracking and management.

.codex/skills/spec-pipeline/SKILL.md

@@ -8,8 +8,7 @@ description: "Stickman Studio feature workflow: UI/UX and architecture specs, im
 1. **Phase 0a: UI/UX Proposal & Alternative Ideas (User-Facing Features Only)**
    - `@uiux` analyzes the user's initial idea for cognitive friction, accessibility, and kid-friendliness.
    - For an in-stage selected-object inspector, `@uiux` first reviews `docs/specs/stage_panel_ui_system.md` and the current shared controls under `scripts/shared/stage_ui/`; proposals should build on that system unless the interaction needs justify a specific exception.
-   - `@uiux` pitches **1–3 alternative interaction approaches** (e.g., comparing floating tooltips vs. top-center banners, custom cursor reticles, or streamlined dialogs).
-   - `@uiux` highlights the most intuitive option with `[Recommended]` and asks up to 3 clarification questions.
+   - Follow the concept-count and visual-mockup protocol in `.codex/agents/uiux.toml`; it also applies when the user asks `@uiux` for ideas outside a formal pipeline run.
    - `@uiux` **STOP:** Waits for user feedback/selection before writing the UI spec.
    - _Bypass Rule:_ If the feature is strictly internal engine/backend logic (e.g., physics, serialization, scanning), skip directly to Phase 1a.