fix: wrap CSI terminal query in with-timeout 0.3s

The blocking read-char in %query-terminal-size could hang if the
terminal doesn't respond to CSI 18 t. Wrapped in
sb-ext:with-timeout 0.3 to abort if no response.

src/backend/classes.lisp

@@ -9,15 +9,14 @@ Returns (values cols rows) or nil."
                                    :fill-pointer 0 :adjustable t)))
       (format t "~C[18t" #\Esc)
       (force-output)
-      ;; Blocking read-char loop — the response arrives immediately
-      (loop with deadline = (+ (get-internal-real-time)
-                               (* internal-time-units-per-second 0.5))
-            while (< (get-internal-real-time) deadline)
-            do (let ((ch (read-char saved nil nil)))
-                 (when ch
-                   (vector-push-extend ch response)
-                   (when (char= ch #\t) (return)))))
-      (when (>= (length response) 8)
+      (handler-case
+          (sb-ext:with-timeout 0.3
+            (loop do (let ((ch (read-char saved nil nil)))
+                       (when ch
+                         (vector-push-extend ch response)
+                         (when (char= ch #\t) (return))))))
+        (sb-ext:timeout ()))
+      (when (>= (length response) 5)
         (let* ((str (subseq response 1))
                (start (or (position #\[ str) 0))
                (after (subseq str (1+ start)))