fix(ir): preserve geometry referencing Unknown/Unresolved colors during baking

[bkfunk]

Summary

PartBufferBundleBuilder::query_mesh in ir/src/part.rs previously matched only ColorReference::Current, ColorReference::Complement, and ColorReference::Color, returning None for the Unknown and Unresolved variants. As a result, any geometry that referenced a color whose definition wasn't (yet) in the catalog was silently dropped during bake_part_from_*, even when a ColorCatalog was provided.

This patch folds Unknown and Unresolved into the same arm as Color, so their geometry is preserved in a dedicated mesh buffer and can be reified later via Part::resolve_colors.

Repro (before the fix)

Baking a part that contains a reference to a color not in the supplied ColorCatalog produces a Part with missing geometry — no warning, no error.

Change

-            (ColorReference::Color(_), _) => {
+            (ColorReference::Color(_) | ColorReference::Unknown(_) | ColorReference::Unresolved(_), _) => {
                 Some(self.colored_meshes.entry(group.clone()).or_default())
             }
-            _ => None,
         }

The wildcard arm is no longer reachable, so it's removed (compiles cleanly because ColorReference only has these four constructors).

Test plan

• cargo check --workspace passes
• Manual: bake a model that references an out-of-catalog color and confirm its geometry is present

[Copilot]

Pull request overview

This PR fixes IR part baking so geometry that references ColorReference::Unknown(_) or ColorReference::Unresolved(_) is no longer silently dropped during baking. This aligns with the codebase’s existing ability to later reify color references (e.g., via Part::resolve_colors) once a ColorCatalog is available.

Changes:

• Treat ColorReference::Unknown(_) and ColorReference::Unresolved(_) the same as ColorReference::Color(_) when selecting a destination mesh buffer during baking.
• Remove the now-unreachable fallback match arm in PartBufferBundleBuilder::query_mesh.

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[bkfunk]

Good catch — addressed in f36398c. query_mesh now returns &mut MeshBuffer directly, the call site is simplified accordingly, and the dead Skipping unknown color group_key branch is gone.