fix(client): address PR #109 review — 6 warnings + 5 suggestions

Star map (W1-W3, S3):
- _process visibility guard + dirty flag (no redraw when hidden/unchanged)
- _system_hash masked to 31-bit positive range
- Extracted _find_nearest_system() shared helper

game_state.gd (W4):
- Inline load() in apply_snapshot() replaces per-tick overhead; safe at
  runtime because script is already in resource cache

Data pipeline (W5-W6):
- Script-relative path resolution via __file__
- --check mode + make check-star-map staleness target

Minor (S1-S2, S5):
- Removed redundant bone_idx assignment
- Simplified double-negative test assertion
- Documented autoload parse-order convention in CLAUDE.md

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/scripts/rendering/character_visual.gd

@@ -331,7 +331,6 @@ func _create_overhead_anchor() -> void:
 		return
 	_overhead_attachment = BoneAttachment3D.new()
 	_overhead_attachment.bone_name = "Head"
-	_overhead_attachment.bone_idx = bone_idx
 	_overhead_attachment.name = "OverheadAttachment"
 	_skeleton.add_child(_overhead_attachment)