fix(showcase): drop all clip directives — procedural is the better showcase

Per review, the retargeted Mixamo clips aren't reliably better than the improved L2-L4
procedural (wrong-exercise semantics like the barbell back squat, retarget artifacts,
missing props). Removed clip directives from all moves so the showcase (landing hero,
playground default, README GIFs) runs the polished procedural on the skinned character.
Clip infrastructure (clips.ts / retarget layer / gitignored FBX) is kept dormant for future use.

Author: a-baran-orhan

playground/public/moves/bicycle-crunch.html

@@ -157,7 +157,6 @@ <h2>The .posecode source</h2>
         angles, not 3D transforms.</p>
       <pre class="code-block"><code>posecode exercise &quot;Bicycle crunch&quot;
   rig humanoid
-  clip &quot;bicycle-crunch&quot;
   pose start = supine
 
   step &quot;Set&quot; 0.8s flow:

playground/public/moves/grapevine.html

@@ -157,7 +157,6 @@ <h2>The .posecode source</h2>
         angles, not 3D transforms.</p>
       <pre class="code-block"><code>posecode exercise &quot;Grapevine&quot;
   rig humanoid
-  clip &quot;shuffling&quot;
   pose start = standing
 
   step &quot;Step out&quot; 0.7s flow:

playground/public/moves/jab-cross.html

@@ -157,7 +157,6 @@ <h2>The .posecode source</h2>
         angles, not 3D transforms.</p>
       <pre class="code-block"><code>posecode exercise &quot;Jab-cross&quot;
   rig humanoid
-  clip &quot;jab-cross&quot;
   pose start = standing
 
   step &quot;Jab&quot; 0.4s settle:

playground/public/moves/walk-cycle.html

@@ -162,7 +162,6 @@ <h2>The .posecode source</h2>
       <pre class="code-block"><code>posecode exercise &quot;Walk &amp; turn&quot;
   rig humanoid
   pose start = standing
-  clip &quot;walk&quot;
 
   step &quot;Step right&quot; 0.7s flow:
     hip_right: flex 30

spec/examples/bicycle-crunch.posecode

@@ -1,6 +1,5 @@
 posecode exercise "Bicycle crunch"
   rig humanoid
-  clip "bicycle-crunch"
   pose start = supine
 
   step "Set" 0.8s flow:

spec/examples/grapevine.posecode

@@ -1,6 +1,5 @@
 posecode exercise "Grapevine"
   rig humanoid
-  clip "shuffling"
   pose start = standing
 
   step "Step out" 0.7s flow:

spec/examples/jab-cross.posecode

@@ -1,6 +1,5 @@
 posecode exercise "Jab-cross"
   rig humanoid
-  clip "jab-cross"
   pose start = standing
 
   step "Jab" 0.4s settle:

spec/examples/walk-cycle.posecode

@@ -1,7 +1,6 @@
 posecode exercise "Walk & turn"
   rig humanoid
   pose start = standing
-  clip "walk"
 
   step "Step right" 0.7s flow:
     hip_right: flex 30