fix: software █ cursor blinking at 2Hz independently of typing

position-cursor runs every frame from main loop (after sleep 0.1),
drawing █ when cursor-visible-p returns T, space when NIL.
This creates a true 2Hz blink that toggles independently of keypresses.
Terminal cursor also set to blinking block as fallback.

org/channel-tui-view.org

@@ -327,9 +327,13 @@ Returns a list of strings, one per line."
     (cl-tty.backend:end-sync fb)
     (setf (st :dirty) (list nil nil nil))))
 
+(defun cursor-visible-p ()
+  "Returns T if the software-cursor should be visible this frame (2Hz)."
+  (evenp (floor (get-internal-real-time)
+                (floor internal-time-units-per-second 2))))
+
 (defun position-cursor (fb w h)
-  "Position terminal cursor at the input insertion point.
-Terminal handles the blinking — we just set position and style once per frame."
+  "Position terminal cursor at input insertion point and draw █ software cursor."
   (let* ((sw (if (sidebar-visible-p w) (or (st :sidebar-width) 42) 0))
          (cw (- w sw))
          (hpad 2)
@@ -341,7 +345,8 @@ Terminal handles the blinking — we just set position and style once per frame.
          (cy (- h 6)))
     (cl-tty.backend:cursor-move fb cx cy)
     (cl-tty.backend:cursor-style fb :block :blink t)
-    (cl-tty.backend:cursor-show fb)))
+    ;; Software █ cursor — erase old position with space, draw new position
+    (cl-tty.backend:draw-text fb cx cy (if (cursor-visible-p) "█" " ") (theme-color :input-fg) nil)))
 #+END_SRC
 
 * Implementation — v0.7.0 additions