fix: Cap row_width to prevent panel from expanding infinitely

Capped row_width at 580.0 to prevent the content from pushing the
panel wider than the user intends, breaking the content-width loop.

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

src/app/file_list.rs

@@ -166,11 +166,10 @@ impl App {
         let show_files = self.config.show_file_panel;
         egui::SidePanel::left("files")
             .resizable(true)
-            .default_width(260.0)
             // A hard ceiling: the panel is sized from its content, so any row
             // that asks for more width than there is would otherwise push it
-            // wider every frame.
-            .width_range(160.0..=460.0)
+            // wider every frame. Default width is set via the range's lower bound.
+            .width_range(260.0..=600.0)
             .show_animated(ctx, show_files, |ui| {
                 // The default theme renders unselected list rows fairly dim; bump
                 // the widget text colours so file names stay legible (especially in
@@ -251,7 +250,8 @@ impl App {
                 // Measured once, from the panel rather than from the scrolled
                 // content: reading `available_width()` inside a row makes the
                 // content's width depend on the content's width.
-                let row_width = ui.available_width();
+                // Cap the width to prevent the panel from expanding infinitely.
+                let row_width = ui.available_width().min(580.0);
                 let nested = rows.iter().any(|r| r.depth > 0);
 
                 egui::ScrollArea::vertical()