fix(tmux): drag in a mouse app (claude, vim) died with "syntax error"

The MouseDrag1Pane binding escaped the inner quotes as \" inside a
single-quoted string. Since tmux 3.0 the backslashes are literal there,
so the branch taken when the pane has mouse tracking on failed to parse:
no selection, "syntax error" in the status line. Plain-shell panes never
hit that branch, which is why only claude/vim panes were affected.

tmux.conf

@@ -166,7 +166,7 @@ bind -T copy-mode-vi WheelUpPane   select-pane \; send-keys -X -N 2 scroll-up
 bind -T copy-mode-vi WheelDownPane select-pane \; send-keys -X -N 2 scroll-down
 bind-key -T copy-mode-vi MouseDown1Pane select-pane -t = \; send-keys -X clear-selection
 bind-key -T copy-mode-vi MouseUp1Pane   select-pane -t = \; send-keys -X cancel
-bind -n MouseDrag1Pane if -Ft= '#{mouse_any_flag}' 'if -Ft= \"#{pane_in_mode}\" \"copy-mode -eM\" \"send-keys -M\"' 'copy-mode -eM'
+bind -n MouseDrag1Pane if -Ft= '#{mouse_any_flag}' 'if -Ft= "#{pane_in_mode}" "copy-mode -eM" "send-keys -M"' 'copy-mode -eM'
 # (note) {{{
 # A plain click (MouseDown then MouseUp, no drag) leaves copy-mode: back to
 #   the prompt, selection dropped. A drag sends MouseDrag/MouseDragEnd instead
@@ -176,6 +176,8 @@ bind -n MouseDrag1Pane if -Ft= '#{mouse_any_flag}' 'if -Ft= \"#{pane_in_mode}\"
 #   MouseDrag1Pane, the only difference is that we use `copy-mode -eM` instead
 #   of `copy-mode -M`, so that WheelDownPane can trigger copy-mode to exit when
 #   copy-mode is entered by MouseDrag1Pane
+# Inner quotes stay plain: `\"` is literal inside '...' since tmux 3.0, and the
+#   mouse-app branch (claude, vim) then dies with "syntax error" on every drag.
 # }}}
 
 bind-key k "split-window -v -b -c '#{pane_current_path}'"