feat(animation): add FullHead convention — opt-in head animation in Full animations

FullStruggle, FullWalk etc. animate body+legs but preserve head tracking.
FullHeadStruggle, FullHeadWalk etc. also animate the head.
The 'Head' keyword in the animation name is the opt-in signal.

src/main/java/com/tiedup/remake/client/gltf/GltfPoseConverter.java

@@ -584,6 +584,10 @@ public final class GltfPoseConverter {
         // The "gltf_" prefix is added by convertClipSelective, so check for "gltf_Full"
         boolean isFullBodyAnimation = animName != null &&
             animName.startsWith("gltf_Full");
+        // Head is protected by default — only enabled as a free bone when the animation
+        // name contains "Head" (e.g., FullHeadStruggle, FullHeadIdle).
+        // This lets artists opt-in per animation without affecting the item's regions.
+        boolean allowFreeHead = isFullBodyAnimation && animName.contains("Head");
 
         String[] allParts = {
             "head",
@@ -606,14 +610,14 @@ public final class GltfPoseConverter {
                     isFullBodyAnimation &&
                     enabledParts.contains(partName) &&
                     partsWithKeyframes.contains(partName) &&
-                    !"head".equals(partName)
+                    (!"head".equals(partName) || allowFreeHead)
                 ) {
                     // Full-body animation: free part WITH keyframes — enable.
                     // The "Full" prefix is the artist's explicit opt-in to animate
                     // bones outside their declared regions.
-                    // EXCEPTION: head is never enabled as a free bone — vanilla head
-                    // tracking (mouse look) is always preserved unless the item
-                    // explicitly owns a head region (HEAD, EYES, EARS, MOUTH).
+                    // Head is protected by default (preserves vanilla head tracking).
+                    // Use "Head" in the animation name (e.g., FullHeadStruggle) to
+                    // explicitly opt-in to head control for that animation.
                     part.fullyEnablePart(false);
                 } else {
                     // Non-Full animation, other item's part, or free part without keyframes.