feat(tui): add Ctrl+←/→ shortcuts to resize files panel

- Update help UI to show “Ctrl+←/→ → resize files panel”.
- Change `set_file_panel_width` to return the clamped width.
- Implement Ctrl+←/→ handling in keyboard input to adjust the files panel width, update status messages, and respect panel collapse state.

crates/owlen-tui/src/chat_app.rs

@@ -1046,10 +1046,12 @@ impl ChatApp {
         self.file_panel_width
     }
 
-    pub fn set_file_panel_width(&mut self, width: u16) {
+    pub fn set_file_panel_width(&mut self, width: u16) -> u16 {
         const MIN_WIDTH: u16 = 24;
         const MAX_WIDTH: u16 = 80;
-        self.file_panel_width = width.clamp(MIN_WIDTH, MAX_WIDTH);
+        let clamped = width.clamp(MIN_WIDTH, MAX_WIDTH);
+        self.file_panel_width = clamped;
+        clamped
     }
 
     pub fn expand_file_panel(&mut self) {
@@ -4157,6 +4159,16 @@ impl ChatApp {
                 let is_symbol_search_key = key.modifiers.contains(KeyModifiers::CONTROL)
                     && key.modifiers.contains(KeyModifiers::SHIFT)
                     && matches!(key.code, KeyCode::Char('p') | KeyCode::Char('P'));
+                let is_resize_left = key.modifiers.contains(KeyModifiers::CONTROL)
+                    && matches!(
+                        key.code,
+                        KeyCode::Left | KeyCode::Char('h') | KeyCode::Char('H')
+                    );
+                let is_resize_right = key.modifiers.contains(KeyModifiers::CONTROL)
+                    && matches!(
+                        key.code,
+                        KeyCode::Right | KeyCode::Char('l') | KeyCode::Char('L')
+                    );
 
                 if is_reveal_active && matches!(self.mode, InputMode::Normal) {
                     self.reveal_active_file();
@@ -4179,6 +4191,23 @@ impl ChatApp {
                     return Ok(AppState::Running);
                 }
 
+                if (is_resize_left || is_resize_right)
+                    && matches!(self.mode, InputMode::Normal)
+                    && !self.is_file_panel_collapsed()
+                {
+                    let current = self.file_panel_width();
+                    let delta: i16 = if is_resize_left { -2 } else { 2 };
+                    let candidate = current.saturating_add_signed(delta);
+                    let adjusted = self.set_file_panel_width(candidate);
+                    if adjusted != current {
+                        self.status = format!("Files panel width: {} cols", adjusted);
+                        self.error = None;
+                    } else {
+                        self.status = "Files panel width unchanged".to_string();
+                    }
+                    return Ok(AppState::Running);
+                }
+
                 if is_symbol_search_key && matches!(self.mode, InputMode::Normal) {
                     self.set_input_mode(InputMode::SymbolSearch);
                     self.symbol_search.clear_query();

crates/owlen-tui/src/ui.rs

@@ -3069,6 +3069,7 @@ fn render_help(frame: &mut Frame<'_>, app: &ChatApp) {
             Line::from("  F1 / ?        → toggle help overlay"),
             Line::from("  :h, :help     → open help from command mode"),
             Line::from("  :files, :explorer → toggle files panel"),
+            Line::from("  Ctrl+←/→      → resize files panel"),
         ],
         1 => vec![
             // Editing
@@ -3181,6 +3182,7 @@ fn render_help(frame: &mut Frame<'_>, app: &ChatApp) {
             Line::from("  :h, :help          → show this help"),
             Line::from("  F1 or ?           → toggle help overlay"),
             Line::from("  :files, :explorer → toggle files panel"),
+            Line::from("  Ctrl+←/→          → resize files panel"),
             Line::from("  :quit              → quit application"),
             Line::from("  Ctrl+C twice       → quit application"),
             Line::from("  :reload            → reload configuration and themes"),