Add new scene files and implement stage impact resolver

- Created three new scene files: `wobble.scene`, `wobble2.scene`, and `wobble3.scene` with various terrain and prop configurations.
- Introduced `stage_impact_resolver.gd` script to manage impact detection and response between props and stickmen.
- Added unit tests for actor blocking overlap to ensure proper interaction with stationary props.

docs/specs/phase_17c_impact_wobble.md

@@ -1,6 +1,6 @@
 # Phase 17c — Impact wobble: architecture and implementation specification
 
-> **Status:** Architecture specified for final user sign-off; implementation has not begun.
+> **Status:** Architecture approved and implementation present; automated behavior verification and in-editor user verification are pending.
 > **Product/UI contract:** [Phase 17 plan](../plans/phase_17_props_for_storytelling.md) and [Impact wobble UI/UX specification](phase_17c_impact_wobble_ui.md).
 > **Scope:** A per-placement Wobble setting, visual sample in EDIT, and a short visual response to meaningful physical hits in PLAY.