fix(blocks): one base point convention for creation, redefine, insert, explode, XCLIP and REFEDIT

world = insert_point + Rot * Scale * (P - base_point). Attribute placement, EXPLODE, XCLIP storage, REFEDIT's working copy, the UCS reframe of attributes and the dynamic-block visibility grip ignored the base point and were offset by Rot*Scale*base. They now share insert_transform_with_base. Creation stores a ZERO base and redefine resets it; a no-op redefine moves nothing; the Block Definition dialog prefills the base from the definition. XCLIP filters stored by older builds keep their old displacement.

src/command.rs

@@ -3035,6 +3035,11 @@ pub trait CadCommand: Send {
         None
     }
 
+    /// Supply the referenced block's insertion base point so the attributes
+    /// the command now owns are placed through the same base-point convention
+    /// as the render path. Default: no-op (no base point).
+    fn attreq_set_block_base(&mut self, _base: codec::types::Vector3) {}
+
     /// After the host commits an ATTREQ insert: keep the command running
     /// (repeated placement) instead of ending it.
     fn attreq_continue(&self) -> bool {