feat: world-grid level materials + real movement test suite

- Generated CC0-style prototype grid textures (0.5 m cells) and a shared
  LevelMaterials factory: world-space triplanar mapping over every code-built
  level (test level, dust2, procedural arena) with the existing color coding
  kept as tints. Readable surfaces at speed instead of flat color boxes;
  materials are cached per tint so identical surfaces batch.
- .gdignore + .gitignore the raw downloaded asset packs in addons/ whose
  overlong paths broke Godot import scans and spammed git warnings.
- Replaced the rotted FSM test file (invalid call(t) on Callables, stateless
  stub nodes, hung forever without quitting) with a real suite: 10 tests
  covering state registration, jump bookkeeping, wall-run momentum
  preservation and upward-carry cap, per-player dash cooldown (regression for
  the old shared static), dash speed stacking, chain soft cap, landing
  events, and slide entry momentum. New headless entrypoint:
  godot --headless --path . -s res://movement/tests/run_fsm_tests.gd

Co-Authored-By: Claude Fable 5 <[email protected]>

scenes/maps/procedural_arena/arena_generator.gd

@@ -176,10 +176,7 @@ func _create_box(node_name: String, pos: Vector3, size: Vector3, color: Color) -
 	mesh.name = "MeshInstance3D"
 	mesh.mesh = BoxMesh.new()
 	mesh.mesh.size = size
-	var mat := StandardMaterial3D.new()
-	mat.albedo_color = color
-	mat.roughness = 0.8
-	mesh.mesh.surface_set_material(0, mat)
+	mesh.mesh.surface_set_material(0, LevelMaterials.tinted(color))
 	body.add_child(mesh)
 	
 	add_child(body)
@@ -206,10 +203,7 @@ func _create_ramp(node_name: String, pos: Vector3, size: Vector3, rot_deg: Vecto
 	mesh.name = "MeshInstance3D"
 	mesh.mesh = BoxMesh.new()
 	mesh.mesh.size = size
-	var mat := StandardMaterial3D.new()
-	mat.albedo_color = color
-	mat.roughness = 0.8
-	mesh.mesh.surface_set_material(0, mat)
+	mesh.mesh.surface_set_material(0, LevelMaterials.tinted(color))
 	body.add_child(mesh)
 	
 	add_child(body)