feat: application icon family (a meshed bracket) drawn with VectorCraft (#37)

cargo xtask app-icon computes an isometric L bracket with a bolt hole and a
structured hexahedral mesh (O-grid around the hole), draws it with
vectorcraft-cli and writes icon.svg/png, small-size artwork, the iconset,
icns, ico, an Icon Composer ModelCraft.icon (floor grid Default/Dark, part,
mesh) and its actool Assets.car. The desktop app uses the 256 px export as
its window icon, falling back to eframe's default if it cannot be decoded.


Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

Co-authored-by: jyviko <2501648+jyviko@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

xtask/src/main.rs

@@ -5,6 +5,7 @@
 //! ATTRIBUTION.md.
 #![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::unimplemented, clippy::todo, clippy::unreachable)]
 
+mod app_icon;
 mod assets;
 mod icons;
 mod layers;
@@ -23,6 +24,9 @@ commands:
   icons [ID…]     draw the toolbar icons from their recipes (assets/icons/src/*.json) with
                   VectorCraft (VECTORCRAFT_CLI, else vectorcraft-cli on the PATH): writes each
                   icon's .vectorcraft source and .svg export
+  app-icon        draw the application icon family (assets/app-icon) with VectorCraft, then
+                  write the iconset, icns, ico and Icon Composer document (macOS: sips,
+                  iconutil, magick; actool for Assets.car when available)
   licences [--check]
                   write THIRD-PARTY-LICENSES.txt (the licences of every shipped crate);
                   --check fails when it is out of date
@@ -44,6 +48,7 @@ fn main() -> ExitCode {
         Some("layers") => cmd_layers(),
         Some("assets") => assets::run(&root()),
         Some("icons") => icons::run(&root(), &rest),
+        Some("app-icon") => app_icon::run(&root()),
         Some("licences") => licences::run(&root(), rest.contains(&"--check")),
         Some("test") => {
             let (cargo_args, test_args) = rest.iter().position(|a| *a == "--").map_or((&rest[..], &[][..]), |i| (&rest[..i], &rest[i + 1..]));