Add drag-and-drop import for .pixstrip-preset files

- Workflow page accepts .pixstrip-preset file drops
- Dropped preset files are imported and applied to current config
- Saved to user presets automatically on successful import

pixstrip-gtk/src/steps/step_workflow.rs

@@ -251,6 +251,26 @@ pub fn build_workflow_page(state: &AppState) -> adw::NavigationPage {
         .child(&scrolled)
         .build();
 
+    // Drop target for .pixstrip-preset files
+    let drop_target = gtk::DropTarget::new(gtk::gio::File::static_type(), gtk::gdk::DragAction::COPY);
+    let jc_drop = state.job_config.clone();
+    drop_target.connect_drop(move |_target, value, _x, _y| {
+        if let Ok(file) = value.get::<gtk::gio::File>() {
+            if let Some(path) = file.path() {
+                if path.extension().and_then(|e| e.to_str()) == Some("pixstrip-preset") {
+                    let store = pixstrip_core::storage::PresetStore::new();
+                    if let Ok(preset) = store.import_from_file(&path) {
+                        apply_preset_to_config(&mut jc_drop.borrow_mut(), &preset);
+                        let _ = store.save(&preset);
+                        return true;
+                    }
+                }
+            }
+        }
+        false
+    });
+    clamp.add_controller(drop_target);
+
     adw::NavigationPage::builder()
         .title("Choose a Workflow")
         .tag("step-workflow")