Layer-Smart-Join entfernt — nie verwendet, auto Phase 2 macht's

- Alt+Click bypass im Cluster-Volume-Select-Handler raus.
- _layer_join_attempt + dJoin-Detection in smart_join.py raus.

Phase 2 automatic handling deckt die Use-Cases ab. Falls Manual-Layer-
Merge spaeter doch noetig: commit 118bc51 hat den Code als Referenz.

rhino/elemente.py

@@ -2778,11 +2778,6 @@ class _ClusterVolumeSelectHandler(Rhino.UI.MouseCallback):
             try:
                 if "Left" not in str(e.MouseButton): return
             except Exception: pass
-            # Alt-Click bypassed Cluster-Swap → user kann Layer-Breps
-            # direkt anwaehlen (= fuer Layer-Smart-Join)
-            try:
-                if bool(e.AltKeyDown): return
-            except Exception: pass
             view = e.View
             if view is None: return
             vp = view.ActiveViewport