Add Bubble Tea TUI with interactive treemap

Cell canvas renderer with frame cache and a perceptual 256-colour
quantizer; responsive geometry (large/medium/small/too-small);
squarified treemap with nested previews, LOD grouping, category
colouring and adaptive labels; spatial arrow navigation with stable
NodeID selection; zoom and breadcrumbs; modal system (info, help,
confirm, save); list, file-type, top-N, scan-info, duplicate and
comparison views; live search/filter; mouse support; move-to-trash.

internal/textutil/text_test.go

@@ -62,3 +62,13 @@ func TestSize(t *testing.T) {
 		t.Errorf("SignedSize got %q", got)
 	}
 }
+
+func TestClustersAgreeWithWidth(t *testing.T) {
+	for _, s := range []string{"abc", "日本", "é", "👨‍👩‍👧", "🎉x", "​"} {
+		n := 0
+		Clusters(s, func(_ string, w int) bool { n += w; return true })
+		if n != Width(s) {
+			t.Errorf("%q: clusters %d width %d", s, n, Width(s))
+		}
+	}
+}