feat(block-editor): select and edit native parameter and action grips

Parameters and Move/Scale action markers were drawn as overlays with no selectable authoring objects. Pick their points, labels or graphics in BEDIT to display editable definition, endpoint, reference and label grips using the existing selection overlay and point-input commands. Show the selected object's coordinates in the Properties panel.

Write edits to the native parameter/grip/action records while preserving graph identities and target bindings. Maintain Rotation radii and oriented grip directions, synchronize visibility lookup data, and retain Basepoint attribute relocation with recorded entity history. Escape cancels edits or clears selection; editor undo/redo and save/discard preserve the native changes.

Validate with self-contained viewport-input and native DWG/DXF persistence regressions, all ten parameter types, action bindings, cancellation and Basepoint attribute undo. Checks: 3 focused, 323 block (6 existing opt-in ignored), 39 dock and 23 viewport tests passed; counts overlap.

Ordinary drawing-reference grips and per-instance saved action evaluation follow in the next milestone.

src/command.rs

@@ -1514,6 +1514,13 @@ impl DimensionPreview {
 /// Returned by every `CadCommand` method to tell main.rs what to do.
 #[allow(dead_code)]
 pub enum CmdResult {
+    EditBlockAuthoring {
+        document: u64,
+        definition: Handle,
+        handle: Handle,
+        part: crate::scene::block_authoring::edit::Part,
+        position: DVec3,
+    },
     PlaceBlockAction {
         document: u64,
         definition: Handle,