feat(assets): seven asset commands + Run dispatch/helpers

check-dupes, clean-dupes, check-mdl, fix-mdl, convert, upscale, compile
behind a single runner indirection, mirroring internal/depot's Run shape.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/assets/checkmdl_test.go

@@ -0,0 +1,32 @@
+package assets
+
+import (
+	"bytes"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestCheckMDL(t *testing.T) {
+	dir := t.TempDir()
+	// Uncompiled ASCII model with a name mismatch.
+	bad := filepath.Join(dir, "foo.mdl")
+	if err := os.WriteFile(bad, []byte("newmodel wrong\nbeginmodelgeom wrong\nendmodelgeom wrong\ndonemodel wrong\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	var out, errw bytes.Buffer
+	if code := runCheckMDL([]string{dir}, &out, &errw); code != exitFail {
+		t.Fatalf("bad mdl exit = %d, want %d\n%s", code, exitFail, errw.String())
+	}
+
+	// A binary (compiled) model is fine.
+	good := t.TempDir()
+	if err := os.WriteFile(filepath.Join(good, "bar.mdl"), []byte("\x00\x00compiled binary blob"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	out.Reset()
+	errw.Reset()
+	if code := runCheckMDL([]string{good}, &out, &errw); code != exitOK {
+		t.Fatalf("binary mdl exit = %d, want %d\n%s", code, exitOK, errw.String())
+	}
+}