feat: extend rig-format with texture/z_order/scale/anchor fields

Additive extension to build_rig output, preserving backward-compat
with existing rigs that lack the new fields:

- bone.texture: optional atlas-id (string) for sprite-mode rendering;
  resolved to a texture-handle by puppet.load_textures(). When absent
  the bone falls back to colored-rect render via draw_rect_rotated.
- bone.z_order: render-sort key (lower = back, higher = front);
  default 0.
- bone.scale: [sx, sy] pair; default [1, 1]; negative components
  mirror the sprite.
- bone.anchor: optional [x, y] override of the atlas-supplied anchor.
- rig.asset_pack: alias-key into the consumer module's asset_aliases
  manifest field; lets puppet.load_textures resolve atlas-ids to
  texture-handles via the asset-lib.
- rig.bones_z_sorted: array of bones pre-sorted by z_order; render
  walks this once per frame.

Version bumped to 0.2.0. Subsequent commits add multi-level parent-
chain transform, sprite-mode render, and load_textures.

manifest.lib

@@ -1,6 +1,6 @@
 {
     "id": "lib-core.puppet",
-    "version": "0.1.0",
+    "version": "0.2.0",
     "api_min": "0.1",
     "deps": []
 }