Add icon preview to drag-and-drop dialog

Fast icon extraction pulls .DirIcon from the squashfs without full
analysis. Single-file drops show a 64px preview in the dialog while
the user chooses an import option.

src/ui/drop_dialog.rs

@@ -6,6 +6,7 @@ use std::rc::Rc;
 use crate::core::analysis;
 use crate::core::database::Database;
 use crate::core::discovery;
+use crate::core::inspector;
 use crate::i18n::{i18n, ni18n_f};
 
 /// Registered file info returned by the fast registration phase.
@@ -63,6 +64,28 @@ pub fn show_drop_dialog(
         .body(&body)
         .build();
 
+    // For single file, try fast icon extraction for a preview
+    if count == 1 {
+        let file_path = files[0].clone();
+        let dialog_ref = dialog.clone();
+        glib::spawn_future_local(async move {
+            let result = gio::spawn_blocking(move || {
+                inspector::extract_icon_fast(&file_path)
+            })
+            .await;
+
+            if let Ok(Some(icon_path)) = result {
+                let image = gtk::Image::builder()
+                    .file(icon_path.to_string_lossy().as_ref())
+                    .pixel_size(64)
+                    .halign(gtk::Align::Center)
+                    .margin_top(12)
+                    .build();
+                dialog_ref.set_extra_child(Some(&image));
+            }
+        });
+    }
+
     dialog.add_response("cancel", &i18n("Cancel"));
     dialog.add_response("keep-in-place", &i18n("Keep in place"));
     dialog.add_response("copy-only", &i18n("Copy to Applications"));