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/tests/test_sprint30.gd

@@ -230,7 +230,7 @@ func test_descriptor_has_no_hair_highlight_tint_field() -> void:
 	assert_bool(d.has("hair_highlight_tint")).override_failure_message(
 		"to_dict() must NOT include hair_highlight_tint — highlight is auto-derived"
 	).is_false()
-	assert_bool(desc.get("hair_highlight_tint") != null and typeof(desc.get("hair_highlight_tint")) != TYPE_NIL).override_failure_message(
+	assert_bool("hair_highlight_tint" in desc).override_failure_message(
 		"CharacterVisualDescriptor must not define a hair_highlight_tint property"
 	).is_false()