feat(client): add tile rendering, fog overlay, and camera smoothing

Sprint 2 rendering pipeline: tiles (#129), fog (#131), camera (#116).

- tile_renderer.gd: programmatic TileSet with floor/wall/door/object
  placeholder tiles, renders from snapshot tile data
- fog_renderer.gd: TileMapLayer overlay with three visibility states
  (visible/fog-edge/hidden), computed from visible_positions data
- Camera2D: smoothing enabled (speed 6.0), 2x zoom, locked to player
- game_state.gd: stores visible_tiles and visible_positions from snapshots
- sim_bridge.gd: test data with 8x8 room, corridor, and Manhattan
  distance visibility for development without server
- Scene render order: Tiles -> FogOverlay -> Entities
- Background clear color set to near-black for unexplored areas

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

client/scripts/autoloads/game_state.gd

@@ -1,11 +1,14 @@
 extends Node
 
-# Updated each frame from ObserverSnapshot data (Protocol format: {tick, entities}).
+# Updated each frame from ObserverSnapshot data (Protocol format: {tick, entities, tiles}).
 # Entities use Protocol decoded format: {entity_id, x, y, z, kind: {variant, data}}.
+# Tiles use format: [{x, y, z, type}].
 var current_snapshot: Dictionary = {}
 var current_tick: int = 0
 var player_position: Vector2 = Vector2.ZERO
 var visible_entities: Array = []
+var visible_tiles: Array = []
+var visible_positions: Dictionary = {}  # Vector2i -> true, for fast fog lookups
 
 # Player entity ID — the first entity is assumed to be the player (will be
 # refined when the server assigns explicit player entity IDs).
@@ -24,3 +27,11 @@ func apply_snapshot(snapshot: Dictionary) -> void:
 			if entity.has("entity_id") and entity.entity_id == player_entity_id:
 				player_position = Vector2(entity.x, entity.y)
 				break
+
+	if snapshot.has("tiles"):
+		visible_tiles = snapshot.tiles
+
+	if snapshot.has("visible_positions"):
+		visible_positions.clear()
+		for pos in snapshot.visible_positions:
+			visible_positions[Vector2i(pos.x, pos.y)] = true