feat(ribbon): contextual Block Editor tab while editing a block

Opening the block editor brings up a Block Editor ribbon tab with
Edit / Save / Discard, Attribute Definition, and the geometric,
dimensional and parameter tools that drive parametric blocks. The tab
is only listed while a block editor session is open, and leaving the
session returns to the tab that was active before.

Refs #509

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

src/modules/mod.rs

@@ -25,6 +25,7 @@ pub use ocs_plugin_api::ribbon::{
 // ── Module declarations ───────────────────────────────────────────────────
 
 pub mod annotate;
+pub mod block_editor;
 pub mod draw;
 pub mod insert;
 pub mod layout;