fix: refocus terminal on window focus

Ctrl input can stop working if the browser window loses focus. Add a
window focus listener to re-focus the terminal whenever the window is
activated, restoring keyboard modifiers without requiring a reload.

src/webterm/static/js/terminal.ts

@@ -608,6 +608,11 @@ class WebTerminal {
         this.terminal.focus();
       }
     });
+
+    // Restore focus when browser window regains focus
+    window.addEventListener("focus", () => {
+      this.terminal.focus();
+    });
   }
 
   /** Setup mobile keyboard input via hidden textarea */