feat: Add geometry module demo system for orbital mechanics

Creates comprehensive visual demonstrations of the geometry module:

Static demos:
- Bresenham algorithms: circle/line rasterization on grid cells
- Angle calculations: line elements showing angles between points,
  waypoint viability with angle thresholds, orbit exit headings
- Pathfinding: planets with surfaces and orbit rings, optimal
  path using orbital slingshots vs direct path comparison

Animated demos:
- Solar system: planets orbiting star with discrete time steps,
  nested moon orbit, position updates every second
- Pathfinding through moving system: ship navigates to target
  using orbital intercepts, anticipating planetary motion

Includes 5 screenshot outputs demonstrating each feature.

Run: ./mcrogueface --headless --exec tests/geometry_demo/geometry_main.py
Interactive: ./mcrogueface tests/geometry_demo/geometry_main.py

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/geometry_demo/screens/__init__.py

@@ -0,0 +1,6 @@
+"""Geometry demo screens."""
+from .bresenham_demo import BresenhamDemo
+from .angle_lines_demo import AngleLinesDemo
+from .pathfinding_static_demo import PathfindingStaticDemo
+from .solar_system_demo import SolarSystemDemo
+from .pathfinding_animated_demo import PathfindingAnimatedDemo