chore: remove dead UI helpers and orphan toolbar stubs

Each item below was gated by #[allow(dead_code)] and has zero callers
across src/ — none of them are part of any public API consumed by
external crates (this is a binary, not a library):

* modules/insert/underlay_frames.rs + edit_aliases.rs — toolbar stubs
  whose `tool()` registrars were never wired into the ribbon; the
  parent mod.rs inlines its own include_bytes! for the SVGs, so the
  files were orphan dead weight.
* ui/snap_popup.rs:snap_marker_color — never called.
* ui/ribbon/mod.rs:last_dropdown_cmd — never called.
* ui/scale_popup.rs:anno_scale_for_label — never called.
* ui/layers.rs:color_name_to_aci — inverse of aci_color_display
  with zero call sites.
* linetypes.rs:name_list — never called.
* scene/pipeline/wire_gpu.rs:new_ghost — never called.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/ui/scale_popup.rs

@@ -23,15 +23,6 @@ const COMMON_SCALES: &[(&str, f32, f64)] = &[
     ("10:1", 0.1, 10.00),
 ];
 
-#[allow(dead_code)]
-pub fn anno_scale_for_label(label: &str) -> f32 {
-    COMMON_SCALES
-        .iter()
-        .find(|&&(l, _, _)| l == label)
-        .map(|&(_, a, _)| a)
-        .unwrap_or(1.0)
-}
-
 /// Full-screen overlay: transparent click-catcher + scale list panel pinned bottom-right.
 ///
 /// - `is_model`: true = model space (dispatches SetAnnotationScale), false = paper space (SetViewportScale).