fix(client): address PR #11 review — type safety, perf, tests

Add Dictionary validation in game_state visible_tiles loop to prevent
crash on malformed data (Hoshe critical). Skip redundant modulate.a
writes (Hoshe suggestion). Add 3 tests: malformed visible_tiles,
facing rotation accuracy, v1 backward compatibility. Clarify D-033
Phase 1/Phase 2 comments.

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

client/scripts/rendering/entity_renderer.gd

@@ -79,11 +79,11 @@ func _update_entity_node(entity_id: int, entity_data: Dictionary) -> void:
 		)
 
 	# v2: Peripheral vision dimming (D-015)
+	# null visibility (v1 backward compat) defaults to full alpha
 	var visibility: Variant = entity_data.get("visibility")
-	if visibility == "Peripheral":
-		entity_node.modulate.a = Constants.PERIPHERAL_ALPHA
-	else:
-		entity_node.modulate.a = 1.0
+	var target_alpha := Constants.PERIPHERAL_ALPHA if visibility == "Peripheral" else 1.0
+	if not is_equal_approx(entity_node.modulate.a, target_alpha):
+		entity_node.modulate.a = target_alpha
 
 	# v2: Update facing indicator rotation (player entity only)
 	if entity_id == GameState.player_entity_id: