feat(puppet): v0.3.0 — idle-return locomotion + version bump

- apply_locomotion idle-return: after (now - last_move_time) >
  idle_return_delay, the most-displaced planted leg steps back to its
  current hip position (over idle_step_duration). Group-stagger via
  bumping last_move_time forward by idle_return_stagger.
- M.move_to tracks p.last_move_time when position actually changes.
- README v0.3.0 changelog entry.

manifest.lib

@@ -1,6 +1,6 @@
 {
     "id": "lib-core.puppet",
-    "version": "0.2.0",
+    "version": "0.3.0",
     "api_min": "0.1",
     "deps": []
 }