Add macos-dock-drop-folder-behavior configuration option

This adds a new configuration option that controls whether folders
dropped onto the Ghostty dock icon open in a new tab (default) or
a new window.

The option accepts two values:
- tab: Opens folders in a new tab in the main window (default)
- window: Opens folders in a new window

This is useful for users who prefer window-based workflows over
tab-based workflows when opening folders via drag and drop.

src/config/Config.zig

@@ -2631,6 +2631,20 @@ keybind: Keybinds = .{},
 /// editor, etc.
 @"macos-titlebar-proxy-icon": MacTitlebarProxyIcon = .visible,
 
+/// Controls the behavior when dropping a folder onto the Ghostty dock icon
+/// on macOS.
+///
+/// Valid values are:
+///
+///   * `tab` - Open the folder in a new tab in the main window (default).
+///   * `window` - Open the folder in a new window.
+///
+/// The default value is `tab`.
+///
+/// This setting is only supported on macOS and has no effect on other
+/// platforms.
+@"macos-dock-drop-folder-behavior": MacOSDockDropFolderBehavior = .tab,
+
 /// macOS doesn't have a distinct "alt" key and instead has the "option"
 /// key which behaves slightly differently. On macOS by default, the
 /// option key plus a character will sometimes produce a Unicode character.
@@ -7082,6 +7096,12 @@ pub const WindowNewTabPosition = enum {
     end,
 };
 
+/// See macos-dock-drop-folder-behavior
+pub const MacOSDockDropFolderBehavior = enum {
+    tab,
+    window,
+};
+
 /// See window-show-tab-bar
 pub const WindowShowTabBar = enum {
     always,