fix: add stty -icanon for character-at-a-time input

Without -icanon, the terminal driver buffers all input until Enter,
so Ctrl+P/B never arrive as individual key events. With -icanon,
cat reads bytes immediately and pipes them to SBCL. SBCL reads from
the pipe, not fd 0, so there's no fd 0 read block issue.

org/channel-tui-main.org

@@ -910,8 +910,13 @@ Event handlers + daemon I/O + main loop.
         ;; breaks read on fd 0 in this SBCL environment, but -echo alone
         ;; works. A cat subprocess inherits the terminal and provides
         ;; bytes through a pipe that SBCL reads reliably.
-         ;; A cat subprocess reads keyboard input from the terminal.
-         (let* ((cat-proc (uiop:launch-program '("stdbuf" "-o0" "cat")
+         ;; Enable character-at-a-time input (-icanon) so Ctrl+P/B
+         ;; arrive as individual bytes instead of being buffered.
+         ;; SBCL now reads from cat's pipe, not directly from fd 0,
+         ;; so -icanon doesn't trigger the SBCL read block issue.
+         (uiop:run-program '("stty" "-icanon" "-echo")
+                           :output nil :ignore-error-status t)
+         (let* ((cat-proc (uiop:launch-program '("cat")
                                               :output :stream
                                               :input :interactive
                                               :stderr nil))