Strip Storm Sewer from plugin-host branch (framework only)

Removes storm_sewer module and stormsewer crate so this branch is suitable for upstream PR. Plugin host, docs, and CadCommand acquisition hooks remain.

src/modules/mod.rs

@@ -140,7 +140,6 @@ pub mod insert;
 pub mod model;
 pub mod layout;
 pub mod manage;
-pub mod storm_sewer;
 pub mod view;
 
 // ── Auto-generated module registry ───────────────────────────────────────