fix(cli): draw grapheme clusters whole in the theme preview

The +list-themes interactive preview dropped the second emoji of ZWJ
clusters (e.g. woman + ZWJ + rocket) in the search box. Zig's libvaxis
enables Unicode grapheme mode 2027 for its session and sizes text per
grapheme cluster; the Rust preview did neither, so the terminal split
the cluster at the ZWJ and the cursor column was computed from summed
per-codepoint widths (4 instead of 2).
- The preview sends ?2027h on entry and ?2027l on exit like vaxis.
- tui::gwidth follows vaxis's unicode width rules per grapheme cluster
  (VS15/VS16, emoji presentation, regional-indicator pairs) using the
  ghostty-unicode emoji table; the preview's print path uses it.
+list-colors and +list-keybinds pretty output (also using gwidth) stays
byte-identical to /usr/bin/ghostty at widths 40/80/132.

Test Plan:
- cargo test -p ghostty-cli --test list_themes_pty
  zwj_emoji_cluster_is_drawn_whole_in_search_box
- cargo test --workspace --no-fail-fast

tests/list_themes_pty.rs

@@ -380,3 +380,10 @@ fn load_file_error_exits_the_preview() {
     }
     assert!(code.is_some(), "the preview must have exited");
 }
+
+#[test]
+fn zwj_emoji_cluster_is_drawn_whole_in_search_box() {
+    let cluster = "\u{1F469}\u{200D}\u{1F680}";
+    let typed = format!("a{cluster}b");
+    check_trace(&[typed.as_bytes()], &[&typed]);
+}