W41: Test for panel focus border flash

The panel_switch_anim system already flashes the active panel
border from theme.info to theme.accent on focus change
(switch_focus). Add an explicit test that verifies the
animation reset-on-switch and the tick-by-tick advance back
to 100, guarding against future refactors breaking the
visual feedback for Tab panel switching.

Tests: 1403 pass (was 1402), zero warnings.

local/recipes/tui/tlc/source/src/filemanager/mod.rs

@@ -1536,6 +1536,27 @@ mod tests {
         let _ = fs::remove_dir_all(&dir);
     }
 
+    #[test]
+    fn switch_focus_resets_panel_switch_animation() {
+        let dir = std::env::temp_dir().join("tlc-fm-switch-focus");
+        let _ = fs::remove_dir_all(&dir);
+        fs::create_dir_all(&dir).unwrap();
+        let mut fm = FileManager::new(&dir, &empty_cfg()).unwrap();
+        // Settled at 100.
+        assert_eq!(fm.panel_switch_anim, 100);
+        // switch_focus resets to 0 so the border flashes info→accent.
+        fm.switch_focus();
+        assert_eq!(fm.panel_switch_anim, 0);
+        // Ticks advance toward 100.
+        fm.sync_animations();
+        assert!(fm.panel_switch_anim > 0);
+        fm.sync_animations();
+        fm.sync_animations();
+        fm.sync_animations();
+        assert_eq!(fm.panel_switch_anim, 100);
+        let _ = fs::remove_dir_all(&dir);
+    }
+
     #[test]
     fn equal_split_resets_ratio() {
         let dir = std::env::temp_dir().join("tlc-fm-split-equal");