feat: rebuild character skin with full 13-clip CC0 animation set

The shipped skin GLB only had Idle/Walk/Run/Jump, so Slide, WallRun, Crouch,
Dash, Fall and Land all fell back to the wrong clips. Rebuilt via the Blender
pipeline from the library-skeleton rigged model (the old miku_proper_anim was
on a different skeleton, so retargeting silently baked flat clips — and the
shooter pose layer's DEF-* bone names never matched it either).

miku.glb now ships Idle, Walk, Run, Sprint, Jump, Fall, Land, CrouchIdle,
CrouchWalk, Dash (roll), Death, Hit, Dance from the Quaternius Universal
Animation Library (CC0). Verified per-bone keyframe motion in the export and
rendered pose stills for deformation QA (no crossed arms / stretched feet).

Also removed five stale experimental skin GLBs + extracted textures and the
one-off editor import scripts; skins.json now lists only the working skin.

Co-Authored-By: Claude Fable 5 <[email protected]>

assets/characters/skins/skins.json

@@ -4,14 +4,7 @@
       "id": "miku",
       "name": "Miku",
       "description": "Hatsune Miku \u2014 Virtual Idol",
-      "model": "res://assets/characters/skins/miku_proper_anim.glb",
-      "unlocked": true
-    },
-    {
-      "id": "miku_test",
-      "name": "Miku Test",
-      "description": "",
-      "model": "res://assets/characters/skins/miku_test.glb",
+      "model": "res://assets/characters/skins/miku.glb",
       "unlocked": true
     }
   ]