hyprland/workspaces: expose workspace name as CSS class

Enable per-workspace styling by adding the workspace name as a
CSS class to each workspace button. The name is sanitized to a
valid CSS identifier: lowercased, non-alphanumeric characters
collapsed to hyphens, digit-leading names prefixed with "ws-".

Examples: "IDE" → .ide, "special:telegram" → .telegram, "1" → .ws-1

Allows users to style individual workspaces:
  #workspaces button.telegram { color: #54a0e0; }

include/modules/hyprland/workspace.hpp

@@ -71,6 +71,7 @@ class Workspace {
 
   int m_id;
   std::string m_name;
+  std::string m_prevNameClass;
   std::string m_output;
   uint m_windows;
   bool m_isActive = false;