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/core/inspector.rs

@@ -603,6 +603,50 @@ fn make_app_id(name: &str) -> String {
         .to_string()
 }
 
+/// Quickly extract just the icon from an AppImage (for preview).
+/// Only extracts .DirIcon and root-level .png/.svg files.
+/// Returns the path to the cached icon if successful.
+pub fn extract_icon_fast(appimage_path: &Path) -> Option<PathBuf> {
+    if !has_unsquashfs() {
+        return None;
+    }
+
+    let offset = find_squashfs_offset(appimage_path).ok()?;
+    let tmp = tempfile::tempdir().ok()?;
+    let dest = tmp.path().join("icon_extract");
+
+    let status = Command::new("unsquashfs")
+        .arg("-offset")
+        .arg(offset.to_string())
+        .arg("-no-progress")
+        .arg("-force")
+        .arg("-dest")
+        .arg(&dest)
+        .arg(appimage_path)
+        .arg(".DirIcon")
+        .arg("*.png")
+        .arg("*.svg")
+        .stdout(std::process::Stdio::null())
+        .stderr(std::process::Stdio::null())
+        .status()
+        .ok()?;
+
+    if !status.success() {
+        return None;
+    }
+
+    let icon_path = find_icon(&dest, None)?;
+
+    // Generate app_id from filename
+    let stem = appimage_path
+        .file_stem()
+        .and_then(|s| s.to_str())
+        .unwrap_or("unknown");
+    let app_id = make_app_id(stem);
+
+    cache_icon(&icon_path, &app_id)
+}
+
 /// Inspect an AppImage and extract its metadata.
 pub fn inspect_appimage(
     path: &Path,