feat(puppet): v0.4.0 — Subterrain control model

Multi-look-target API: set_look_target(handle, target_id, x, y),
clear_look_target(handle, target_id). Bones declare look_at as string
target-id; legacy look_at=true maps to target_id="default". Slerp-style
smoothing: look_at_slerp field (exponential approach, clamped to [0,1]
per frame). Linear look_at_speed kept for backward-compat. Virtual bone
flag: virtual=true skips render pass but participates in compute_world.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

manifest.lib

@@ -1,6 +1,6 @@
 {
     "id": "lib-core.puppet",
-    "version": "0.3.3",
+    "version": "0.4.0",
     "api_min": "0.1",
     "deps": []
 }