Start with all directories collapsed

- Directories now start collapsed by default (vifm-style)
- User must press 'l' to expand directories
- Preserves expanded state during rescan
- Remove unused collect_all_dirs function

src/state/mod.rs

@@ -34,9 +34,8 @@ pub struct FlattenedItem {
 
 impl AppState {
     pub fn new(cache: Cache, config: Config) -> Self {
-        let mut expanded_dirs = HashSet::new();
+        // Start with all directories collapsed (vifm-style)
-        // Start with all directories expanded
+        let expanded_dirs = HashSet::new();
-        collect_all_dirs(&cache.file_tree, &mut expanded_dirs);
 
         let flattened_items = flatten_tree(&cache.file_tree, 0, &expanded_dirs);
 
@@ -107,8 +106,7 @@ impl AppState {
     }
 
     pub fn refresh_flattened_items(&mut self) {
-        self.expanded_dirs.clear();
+        // Keep current expanded state after rescan
-        collect_all_dirs(&self.cache.file_tree, &mut self.expanded_dirs);
         self.rebuild_flattened_items();
     }
 
@@ -139,12 +137,3 @@ fn flatten_tree(nodes: &[FileTreeNode], depth: usize, expanded_dirs: &HashSet<Pa
 
     result
 }
-
-fn collect_all_dirs(nodes: &[FileTreeNode], dirs: &mut HashSet<PathBuf>) {
-    for node in nodes {
-        if node.is_dir {
-            dirs.insert(node.path.clone());
-            collect_all_dirs(&node.children, dirs);
-        }
-    }
-}