Add vim bindings and directory expand/collapse

- Replace arrow keys with j/k for navigation
- Add h/l for collapse/expand directories
- Remove emoji icons, use clean text markers
- Show directories with [-]/[+] expand markers
- Track expanded state per directory path
- Add directory suffix (/) for clarity
- Update help text with vim bindings

src/main.rs

@@ -101,12 +101,18 @@ async fn handle_key_event(state: &mut AppState, key_code: KeyCode) -> Result<()>
         KeyCode::Char('q') => {
             state.should_quit = true;
         }
-        KeyCode::Up => {
+        KeyCode::Char('k') => {
             state.move_selection_up();
         }
-        KeyCode::Down => {
+        KeyCode::Char('j') => {
             state.move_selection_down();
         }
+        KeyCode::Char('h') => {
+            state.collapse_selected();
+        }
+        KeyCode::Char('l') => {
+            state.expand_selected();
+        }
         KeyCode::Enter => {
             if let Some(item) = state.get_selected_item() {
                 if !item.node.is_dir {

src/state/mod.rs

@@ -1,5 +1,6 @@
 use crate::cache::{Cache, FileTreeNode};
 use crate::config::Config;
+use std::collections::HashSet;
 use std::path::PathBuf;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -21,6 +22,7 @@ pub struct AppState {
     pub volume: i64,
     pub should_quit: bool,
     pub flattened_items: Vec<FlattenedItem>,
+    pub expanded_dirs: HashSet<PathBuf>,
 }
 
 #[derive(Debug, Clone)]
@@ -32,7 +34,11 @@ pub struct FlattenedItem {
 
 impl AppState {
     pub fn new(cache: Cache, config: Config) -> Self {
-        let flattened_items = flatten_tree(&cache.file_tree, 0);
+        let mut expanded_dirs = HashSet::new();
+        // Start with all directories expanded
+        collect_all_dirs(&cache.file_tree, &mut expanded_dirs);
+
+        let flattened_items = flatten_tree(&cache.file_tree, 0, &expanded_dirs);
 
         Self {
             cache,
@@ -46,6 +52,7 @@ impl AppState {
             volume: 100,
             should_quit: false,
             flattened_items,
+            expanded_dirs,
         }
     }
 
@@ -65,28 +72,79 @@ impl AppState {
         self.flattened_items.get(self.selected_index)
     }
 
+    pub fn toggle_expand(&mut self) {
+        if let Some(item) = self.get_selected_item() {
+            if item.node.is_dir {
+                let path = item.node.path.clone();
+                if self.expanded_dirs.contains(&path) {
+                    self.expanded_dirs.remove(&path);
+                } else {
+                    self.expanded_dirs.insert(path);
+                }
+                self.rebuild_flattened_items();
+            }
+        }
+    }
+
+    pub fn collapse_selected(&mut self) {
+        if let Some(item) = self.get_selected_item() {
+            if item.node.is_dir {
+                let path = item.node.path.clone();
+                self.expanded_dirs.remove(&path);
+                self.rebuild_flattened_items();
+            }
+        }
+    }
+
+    pub fn expand_selected(&mut self) {
+        if let Some(item) = self.get_selected_item() {
+            if item.node.is_dir {
+                let path = item.node.path.clone();
+                self.expanded_dirs.insert(path);
+                self.rebuild_flattened_items();
+            }
+        }
+    }
+
     pub fn refresh_flattened_items(&mut self) {
-        self.flattened_items = flatten_tree(&self.cache.file_tree, 0);
+        self.expanded_dirs.clear();
+        collect_all_dirs(&self.cache.file_tree, &mut self.expanded_dirs);
+        self.rebuild_flattened_items();
+    }
+
+    fn rebuild_flattened_items(&mut self) {
+        self.flattened_items = flatten_tree(&self.cache.file_tree, 0, &self.expanded_dirs);
         if self.selected_index >= self.flattened_items.len() {
             self.selected_index = self.flattened_items.len().saturating_sub(1);
         }
     }
 }
 
-fn flatten_tree(nodes: &[FileTreeNode], depth: usize) -> Vec<FlattenedItem> {
+fn flatten_tree(nodes: &[FileTreeNode], depth: usize, expanded_dirs: &HashSet<PathBuf>) -> Vec<FlattenedItem> {
     let mut result = Vec::new();
 
     for node in nodes {
+        let is_expanded = expanded_dirs.contains(&node.path);
+
         result.push(FlattenedItem {
             node: node.clone(),
             depth,
-            is_expanded: true, // For now, all directories are expanded
+            is_expanded,
         });
 
-        if node.is_dir && !node.children.is_empty() {
-            result.extend(flatten_tree(&node.children, depth + 1));
+        if node.is_dir && !node.children.is_empty() && is_expanded {
+            result.extend(flatten_tree(&node.children, depth + 1, expanded_dirs));
         }
     }
 
     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);
+        }
+    }
+}

src/ui/mod.rs

@@ -24,8 +24,13 @@ fn render_file_panel(frame: &mut Frame, state: &AppState, area: Rect) {
         .enumerate()
         .map(|(idx, item)| {
             let indent = "  ".repeat(item.depth);
-            let prefix = if item.node.is_dir { "📁 " } else if item.node.metadata.as_ref().map(|m| m.is_video).unwrap_or(false) { "🎥 " } else { "🎵 " };
-            let text = format!("{}{}{}", indent, prefix, item.node.name);
+            let expand_marker = if item.node.is_dir {
+                if item.is_expanded { "[-] " } else { "[+] " }
+            } else {
+                "    "
+            };
+            let suffix = if item.node.is_dir { "/" } else { "" };
+            let text = format!("{}{}{}{}", indent, expand_marker, item.node.name, suffix);
 
             let style = if idx == state.selected_index {
                 Style::default().fg(Color::Black).bg(Color::Cyan)
@@ -114,12 +119,16 @@ fn render_status_panel(frame: &mut Frame, state: &AppState, area: Rect) {
     let help_text = vec![
         Line::from(""),
         Line::from(vec![
-            Span::styled("↑/↓", Style::default().fg(Color::Cyan)),
-            Span::raw(" Navigate"),
+            Span::styled("j/k", Style::default().fg(Color::Cyan)),
+            Span::raw(" Navigate down/up"),
+        ]),
+        Line::from(vec![
+            Span::styled("h/l", Style::default().fg(Color::Cyan)),
+            Span::raw(" Collapse/expand dir"),
         ]),
         Line::from(vec![
             Span::styled("Enter", Style::default().fg(Color::Cyan)),
-            Span::raw(" Play"),
+            Span::raw(" Play file"),
         ]),
         Line::from(vec![
             Span::styled("Space", Style::default().fg(Color::Cyan)),