Clear history when clearing a pane

Helpful if the pane is resized to prevent cleared lines from returning.

scripts/wk/ui/tmux.py

@@ -26,12 +26,16 @@ def capture_pane(pane_id=None):
 
 def clear_pane(pane_id=None):
   """Clear pane buffer for current or target pane."""
-  cmd = ['tmux', 'send-keys', '-R']
+  commands = [
+    ['tmux', 'send-keys', '-R'],
+    ['tmux', 'clear-history'],
+    ]
   if pane_id:
-    cmd.extend(['-t', pane_id])
+    commands = [[*cmd, '-t', pane_id] for cmd in commands]
 
   # Clear pane
-  run_program(cmd, check=False)
+  for cmd in commands:
+    run_program(cmd, check=False)
 
 
 def fix_layout(layout, forced=False):