fix: add missing keyword clause in printable branch of on-key

The revert removed the (keyword ...) clause from the typecase in
on-key's printable branch. Keyword symbols from the main loop
(:a, :h, etc.) fell through to (t nil), making all character input
silently ignored. Typing and sending now works correctly.

lisp/channel-tui-main.lisp

@@ -564,10 +564,12 @@
         (setf (st :dirty) (list nil t nil)))
        ;; Printable
        (t
-        (let ((chr (typecase ch
-                     (character ch)
-                     (integer (code-char ch))
-                     (t nil))))
+         (let ((chr (typecase ch
+                      (character ch)
+                      ((integer 32 126) (code-char ch))
+                      (keyword (let ((s (string ch)))
+                                 (and (= (length s) 1) (char-downcase (char s 0)))))
+                      (t nil))))
           (when (and chr (graphic-char-p chr))
             (input-insert-char chr)
             (setf (st :dirty) (list nil nil t)))))))