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/main.gd

@@ -21,8 +21,9 @@ func _process(_delta: float) -> void:
 		if world_renderer and world_renderer.has_method("update_from_state"):
 			world_renderer.update_from_state()
 
-		# Track camera to player position (D-015)
-		camera.position = GameState.player_position * 32  # tile-space to pixel-space
+	# Track camera to player position every frame (D-015: locked, no panning)
+	# Camera2D smoothing handles interpolation — we just set the target
+	camera.global_position = GameState.player_position * 32.0
 
 	# Send queued input to simulation
 	var inputs = InputMapper.flush_queue()