fix: Set temporary file_uuid for files without SHA256

Problem:
- File nodes had null file_uuid
- Clicking files in UI showed nothing (showDetail() returned early)
- User could not view file details

Solution:
- Set file_uuid to node_id (temporary value) during scan
- Even without SHA256 hash, files can be clicked
- file_uuid will be updated when hash is calculated

Result:
- All files have file_uuid ✅
- Clicking files shows detail panel ✅
- UI fully functional ✅

Files:
- src/scan.rs (file_uuid = node_id)

src/scan.rs

@@ -146,8 +146,6 @@ pub fn scan_directory(user_id: &str, dir: &str, batch_size: usize, options: Scan
         
         let node_id = generate_uuid(path_str, filename, &mac, mtime_secs);
         
-        file_info.push((node_id.clone(), path_str.clone()));
-        
         let file_dir = Path::new(path_str).parent().unwrap_or(dir_path);
         let parent_node_id = if file_dir == dir_path {
             Some(root_node_id.clone())
@@ -155,15 +153,19 @@ pub fn scan_directory(user_id: &str, dir: &str, batch_size: usize, options: Scan
             folder_id_map.get(file_dir.to_string_lossy().as_ref()).cloned()
         };
         
+        let node_id_clone = node_id.clone();
+        
+        file_info.push((node_id_clone.clone(), path_str.clone()));
+        
         file_nodes.push(FileNode {
-            node_id,
+            node_id: node_id_clone.clone(),
             label: filename.clone(),
             aliases: {
                 let mut aliases = Aliases::empty();
                 aliases.set("path", path_str);
                 aliases
             },
-            file_uuid: None,
+            file_uuid: Some(node_id_clone.clone()),
             sha256: None,
             parent_id: parent_node_id,
             children: Vec::new(),