refactor: replace build.rs module codegen with a static registry

The core ribbon registry no longer needs build-time generation. Replace
the generated all_modules() (included from OUT_DIR) with a hand-written
static list in src/modules/registry.rs, listing the seven built-in tabs
in display order.

Trim build.rs down to its only remaining job: embedding the Windows
executable icon via winresource (issue #107). The external plugin system
is unaffected — plugin::registry still appends dynamically-loaded add-on
tabs on top of the core list.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/modules/registry.rs

@@ -1,4 +1,24 @@
-// AUTO-GENERATED include — see build.rs for the actual generator.
-// The generated registry is written to Cargo's OUT_DIR and included here so
-// the source tree is not modified during build.
-include!(concat!(env!("OUT_DIR"), "/modules_registry.rs"));
+// Core ribbon module registry — one boxed instance of every built-in CAD
+// module, in ribbon-tab display order. External add-ons are appended on top
+// of this list at runtime by `plugin::registry`.
+//
+// To add a core module:
+//   1. Create src/modules/my_name/mod.rs  (implement CadModule as MyNameModule)
+//   2. Add `pub mod my_name;` to src/modules/mod.rs
+//   3. Add one `Box::new(super::my_name::MyNameModule)` line below, in the
+//      position you want its tab to appear.
+use crate::modules::CadModule;
+
+/// Returns one boxed instance of every registered core CAD module.
+/// Called once at startup by `Ribbon::new()`.
+pub fn all_modules() -> Vec<Box<dyn CadModule>> {
+    vec![
+        Box::new(super::draw::DrawModule),
+        Box::new(super::model::ModelModule),
+        Box::new(super::insert::InsertModule),
+        Box::new(super::annotate::AnnotateModule),
+        Box::new(super::view::ViewModule),
+        Box::new(super::manage::ManageModule),
+        Box::new(super::layout::LayoutModule),
+    ]
+}