Blocks palette: tabs, options, drag insertion and -INSERT

Rebuild the Blocks palette with Current Drawing / Recent / Favorites /
Libraries tabs, wildcard filter, six views, insertion options, click and
drop insertion and a block context menu. INSERT opens the palette, the
new -INSERT runs on the command line, the ribbon Insert button becomes a
block gallery, and BLOCKMRULIST, BLOCKREDEFINEMODE, BLOCKNAVIGATE,
BLOCKSTATE, EXPLMODE and INSNAME are added.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/command.rs

@@ -1888,6 +1888,12 @@ pub enum CmdResult {
     ReportError(String),
     /// Reports an error and ends the command (`Lines are parallel.`).
     CancelWithMessage(String),
+    /// Explode this block reference and commit its pieces; end the command
+    /// unless `keep_going` (repeated placement).
+    CommitExplodedInsert {
+        insert: EntityType,
+        keep_going: bool,
+    },
     /// Print a measurement result, clear the current selection, and keep the command active.
     ReportMeasurementAndDeselect(String),
     /// Clear the current selection and keep the command active at its updated step.
@@ -2926,6 +2932,12 @@ pub trait CadCommand: Send {
         None
     }
 
+    /// After the host commits an ATTREQ insert: keep the command running
+    /// (repeated placement) instead of ending it.
+    fn attreq_continue(&self) -> bool {
+        false
+    }
+
     /// Returns the INSERT entity built so far (pending attr fill) if this is an
     /// ATTREQ-aware INSERT command waiting for attdef injection.
     /// Called by the host after `AttreqNeeded` to commit the completed Insert.