feat: Add project roadmap and initial specifications for dynamic vector props and terrain system

- Created ROADMAP.md outlining core features, implementation phases, and detailed breakdown for the Stickman Sandbox Builder project.
- Introduced plans for dynamic vector props with `PropBlock` specification, including reusable components and utility functions for prop creation.
- Developed a vector terrain system plan detailing the reusable `TerrainBlock` component and associated utility functions for geometry handling.
- Implemented `PhysicsTestHarness` scene for testing physics interactions with dynamic props and terrain.
- Added scripts for `PropBlock`, `PropUtils`, `TerrainBlock`, and `TerrainUtils` to support dynamic prop creation and terrain management.

plans/VECTOR_TERRAIN_SYSTEM.md

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+## Vector Terrain System
+
+Now that stickmen can be spawned, we need to implement a world for the character.
+We want the world to be based on vector graphics so that camera zooming and panning as smooth and crisp.
+According to ROADMAP.md, we want to start with vector terrains.
+
+The following phases need work:
+
+### Phase 1. Reusable TerrainBlock Component (StaticBody2D)
+
+- Node Hierarchy: A root StaticBody2D with three direct children: Polygon2D for interior fill, Line2D for crisp vector borders, and CollisionPolygon2D for physics boundaries.
+- Property Exposure: An @tool script exposing exported properties for polygon_points (PackedVector2Array), fill_color, outline_color, and outline_width.
+- Auto-Update Logic: A unified property setter that pushes vertex changes directly to Polygon2D and CollisionPolygon2D (configured with BUILD_SOLIDS), while automatically appending the first vertex to the end of Line2D to close the border loop with rounded line joints.
+
+### Phase 2. PhysicsTestHarness Test Scene
+
+- Scene Layout: A standalone test root containing a Camera2D, an environment container with flat ground, angled ramps, and stepped TerrainBlock instances, plus an instantiated MasterRig.
+- Camera Verification: A simple input script on Camera2D that scales zoom levels between 0.25x and 3.0x on mouse wheel scroll to test resolution independence and vector outline thickness.
+
+### Phase 3. TerrainUtils Geometry Engine
+
+- Point Sanitization: A static utility class that processes raw input points by applying grid snapping, running Geometry2D.simplify_polyline() to remove redundant nodes, and enforcing clockwise vertex ordering via Geometry2D.is_polygon_clockwise() for solid collision detection.
+- Factory Spawner: A helper function that takes user input vectors, processes them through the sanitization pipeline, creates a new TerrainBlock instance, applies the cleaned points, and adds it to the target container.