feat(tmux): add layout prefix mode with multiple pane layouts

Add Prefix + Backspace + [number] for quick layout selection:
- 1: Dev layout (4-pane for agentic coding)
- 2: 2x2 grid
- 3: 3x3 grid (using tiled layout)

Author: vanducng

dotfiles/tmux/.tmux.conf

@@ -143,8 +143,12 @@ bind-key -T dev_prefix 7 if -F '#{&&:#{window_zoomed_flag},#{!=:#{pane_index},7}
 bind-key -T dev_prefix 8 if -F '#{&&:#{window_zoomed_flag},#{!=:#{pane_index},8}}' 'select-pane -t 8; resize-pane -Z; switch-client -T dev_prefix' 'select-pane -t 8; switch-client -T dev_prefix'
 bind-key -T dev_prefix 9 if -F '#{&&:#{window_zoomed_flag},#{!=:#{pane_index},9}}' 'select-pane -t 9; resize-pane -Z; switch-client -T dev_prefix' 'select-pane -t 9; switch-client -T dev_prefix'
 
-# Development layout creator (Prefix + Backspace)
-# Creates 4-pane layout for agentic coding:
+# -----------------------------------------------------------------------------------------------------
+# LAYOUT PREFIX MODE (Prefix + Backspace + [number])
+# -----------------------------------------------------------------------------------------------------
+bind-key BSpace switch-client -T layout_prefix
+
+# Layout 1: Dev layout for agentic coding
 # +-------+-------------------+
 # |       |                   |
 # |   0   |    1: editor      |
@@ -155,7 +159,29 @@ bind-key -T dev_prefix 9 if -F '#{&&:#{window_zoomed_flag},#{!=:#{pane_index},9}
 # |       |  cmd1  |   cmd2   |
 # |       | (25%)  |  (25%)   |
 # +-------+--------+----------+
-bind-key BSpace split-window -h -c '#{pane_current_path}' \; resize-pane -x 50% \; split-window -v -c '#{pane_current_path}' \; resize-pane -y 25% \; split-window -h -c '#{pane_current_path}' \; select-pane -t 1
+bind-key -T layout_prefix 1 split-window -h -c '#{pane_current_path}' \; resize-pane -x 50% \; split-window -v -c '#{pane_current_path}' \; resize-pane -y 25% \; split-window -h -c '#{pane_current_path}' \; select-pane -t 0
+
+# Layout 2: 2x2 grid
+# +-------+-------+
+# |   0   |   1   |
+# +-------+-------+
+# |   2   |   3   |
+# +-------+-------+
+bind-key -T layout_prefix 2 split-window -h -c '#{pane_current_path}' \; select-pane -t 0 \; split-window -v -c '#{pane_current_path}' \; select-pane -t 2 \; split-window -v -c '#{pane_current_path}' \; select-pane -t 0
+
+# Layout 3: 3x3 grid (uses tiled layout for even distribution)
+# +-------+-------+-------+
+# |   0   |   3   |   4   |
+# +-------+-------+-------+
+# |   1   |   5   |   6   |
+# +-------+-------+-------+
+# |   2   |   7   |   8   |
+# +-------+-------+-------+
+bind-key -T layout_prefix 3 split-window -v -c '#{pane_current_path}' \; split-window -v -c '#{pane_current_path}' \; select-pane -t 0 \; split-window -h -c '#{pane_current_path}' \; split-window -h -c '#{pane_current_path}' \; select-pane -t 1 \; split-window -h -c '#{pane_current_path}' \; split-window -h -c '#{pane_current_path}' \; select-pane -t 2 \; split-window -h -c '#{pane_current_path}' \; split-window -h -c '#{pane_current_path}' \; select-layout tiled \; select-pane -t 0
+
+# Exit layout prefix mode
+bind-key -T layout_prefix Escape switch-client -T root
+bind-key -T layout_prefix q switch-client -T root
 
 # Exit dev prefix mode with Escape or q
 bind-key -T dev_prefix Escape switch-client -T root