fix(iso): infer facing (not always down) + render features as tiles not avatars

Two iso bugs from reusing the tavern renderer for the SP dungeon:
- Character always faced down/SW: sceneFromGameState hardcoded facing:"down", so the renderers
  ignored their movement-inferred facing (truthy default won). Now facing defaults to null (SP
  server sends none) so iso/3D infer it from movement; facingDelta(null)=down keeps tiled fine.
- "Copy of himself at the origin": the iso renderer drew EVERY entity via _charFrame, so the
  entrance feature rendered as a male character at the start. Features/items now draw as pack tiles
  (stairs/chest) or a glyph; monsters get a red tint so they do not read as a second player.

html/js/render/sceneModel.js

@@ -251,7 +251,9 @@ function sceneFromGameState(state, opts) {
         var playerEntity = {
             id: 'player', x: state.player.x, y: state.player.y,
             kind: 'player', char: '@', color: '#9aa4b2',
-            facing: state.player.facing || 'down', label: null,
+            // No bogus default: the SP server doesn't send facing, so leave it null and let the iso/3D
+            // renderers INFER facing from movement. A hardcoded 'down' made them always face down/SW.
+            facing: state.player.facing || null, label: null,
             you: !state.isSpectating
         };
         // Attach the player's appearance if available (for render-kit character rendering).