Desktop: let HTML5 file drops reach the webview

Tauri v2 intercepts drag-and-drop by default, so the chat's drop overlay
never saw dropped files. Disable its handler on the main window.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

desktop/src-tauri/src/lib.rs

@@ -146,6 +146,8 @@ pub fn run() {
                 .title("Simba")
                 .inner_size(1200.0, 820.0)
                 .min_inner_size(420.0, 520.0)
+                // Let HTML5 drag-and-drop reach the webview (file drop in chat).
+                .disable_drag_drop_handler()
                 .build()?;
             build_tray(app.handle())?;
             register_hotkey(app.handle())?;