Add right-click menu to reorder or unpin favs

Right-clicking a fav tile now opens a small
context menu with Move left, Move right, and
Unpin, instead of relying on drag-only reorder.

- speeddial.js: oncontextmenu handler, the
  menu build/position/dismiss logic, and an
  Escape-key close.
- style.css: .ctx-menu/.ctx-item styling.
- ActionRegistry: reorder_favourites persists
  the new bar order to AppConfig.
- SpeedDialDialog: routes the new
  reorder_favourites command from the page.

src/slic3r/GUI/ActionRegistry.hpp

@@ -58,6 +58,7 @@ public:
     // Dispatch + write-through (registry is the only thing that touches AppConfig).
     ScriptRunOutcome run(const std::string& id);            // runs + bumps stats
     void             set_favourite(const std::string& id, bool on);
+    void             reorder_favourites(const std::vector<std::string>& ids);   // persist a new bar order
 
     bool should_ask(const std::string& plugin_key) const;   // run-confirm gate
     void suppress_ask(const std::string& plugin_key);