fix(client): address PR review — invalidation, constants, tests

Review feedback from Hoshe + Tyre on PR #8:

- Extract shared TILE_SIZE to Constants class_name (Tyre #5, Hoshe #7)
- Fix tile invalidation: detect tile/visibility count changes instead
  of one-shot dirty flag, supports chunk loading (Tyre #3, #4)
- Fog dirty tracking: only re-render when visible_positions changes
- Add bounds warning for unknown tile types (Hoshe #1)
- Add player-not-found warning in GameState (Hoshe #5)
- Use Image.fill_rect() instead of pixel loops (Tyre #10)
- Document _player_pos as reserved for fog decay #113 (Tyre #6)
- Add TODO(#130) for D-033 relationship colors (Hoshe #3, Tyre #8)
- Add class_name to EntityRenderer, FogRenderer, TileRenderer
- 20 new rendering tests (D-030 Layer 1): entity lifecycle, fog
  registration, tile type mapping, snapshot completeness, constants
- 65 total tests passing, 0 failures

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

client/scripts/rendering/entity_renderer.gd

@@ -1,10 +1,11 @@
+class_name EntityRenderer
 extends Node2D
 
 # Entity renderer — manages entity sprites under the Entities node
 # Creates/updates/removes ColorRect children based on entity data
 # Entity format (from Protocol): {entity_id, x, y, z, kind: {variant, data}}
 
-const TILE_SIZE: int = 32
+const TILE_SIZE: int = Constants.TILE_SIZE
 const ENTITY_SIZE: int = 24
 const ENTITY_OFFSET: float = (TILE_SIZE - ENTITY_SIZE) / 2.0  # center within tile
 
@@ -47,13 +48,14 @@ func _create_entity_node(entity_id: int, entity_data: Dictionary) -> void:
 	entity_node.size = Vector2(ENTITY_SIZE, ENTITY_SIZE)
 	entity_node.pivot_offset = Vector2(ENTITY_SIZE / 2.0, ENTITY_SIZE / 2.0)
 
-	# Color based on entity kind (from Protocol decoded format)
+	# Color based on entity kind (from Protocol decoded format).
+	# TODO(#130): replace with D-033 relationship colors (teal/green/amber/red).
 	var kind_variant: String = entity_data.get("kind", {}).get("variant", "")
 	match kind_variant:
 		"Npc":
-			entity_node.color = Color(0.3, 0.6, 0.9)  # Blue for NPCs
+			entity_node.color = Color(0.3, 0.6, 0.9)  # Placeholder blue
 		"Player":
-			entity_node.color = Color(0.88, 0.91, 1.0)  # Light blue for player
+			entity_node.color = Color(0.88, 0.91, 1.0)  # Placeholder light blue
 		_:
 			entity_node.color = Color(0.8, 0.8, 0.8)  # Gray for unknown