Implement Phase 17a Prop Roles UI/UX Specification and associated functionality

- Added UI/UX specification for prop roles and set down mechanics in phase 17a.
- Created `PropStageRoles` script to manage normalized behavior for props, including depth, motion, and collision settings.
- Introduced `StagePhysicsPolicy` for shared physics configurations related to props and actors.
- Developed comprehensive tests for prop roles, including default settings, legacy migration, serialization, and runtime behavior.
- Ensured proper handling of set down actions, including clearance and orientation preservation.

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

@@ -7,6 +7,7 @@ description: "Lean implementation loop: UI/UX (Ideas -> Spec) -> Architect (Clar
 
 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.
    - `@uiux` **STOP:** Waits for user feedback/selection before writing the UI spec.
@@ -15,9 +16,11 @@ description: "Lean implementation loop: UI/UX (Ideas -> Spec) -> Architect (Clar
 2. **Phase 0b: UI Spec Generation**
    - User approves an option or provides feedback.
    - `@uiux` outputs the UI/UX specification (control layouts, widget behaviors, visual feedback states, and cursor logic).
+   - For Stage inspector work, name which shared components and theme tokens the design uses or proposes to extend. Treat dialogs and other editor panels as separate workflows unless their interaction model fits the inspector kit.
 
 3. **Phase 1a: Architecture Proposal & Clarification**
    - `@architect` analyzes existing patterns and the Phase 0b UI/UX specification.
+   - For Stage inspector work, `@architect` inspects the shared panel implementation and theme as well as the design spec, and identifies reuse or justified extension before proposing new controls.
    - `@architect` pitches 1–3 Godot best-practice implementation options and asks up to 3 clarification questions with `[Recommended]` choices.
    - `@architect` stops without writing the spec file yet.