feat: add theme selection palette

Also, refactor to share palette code and make palettes scroll properly
with the mouse wheel.

src/tui/mode/input/vim/visual.zig

@@ -306,6 +306,7 @@ fn mapFollower(self: *Self, keypress: u32, egc: u32, modifiers: u32) !void {
                     'U' => self.cmd("delete_to_begin", .{}),
                     'K' => self.cmd("delete_to_end", .{}),
                     'D' => self.cmd("move_cursor_next_match", .{}),
+                    'T' => self.cmd("change_theme", .{}),
                     else => {},
                 },
                 else => {},
@@ -540,6 +541,7 @@ const hints = tui.KeybindHints.initComptime(.{
     .{ "select_right", "S-right" },
     .{ "select_scroll_down", "C-S-down" },
     .{ "select_scroll_up", "C-S-up" },
+    .{ "change_theme", "C-k C-t" },
     .{ "select_up", "S-up" },
     .{ "select_word_left", "C-S-left" },
     .{ "select_word_right", "C-S-right" },