feat(tmux): add 3-pane split layout template

[merlinsbeard]

Summary

• Add new tmux keybinding prefix + G (Shift+G) for a 3-pane split layout
• Fix tmux deploy path from ~/.tmux.conf to ~/.config/tmux/tmux.conf
• Increase tmux history limit to 1M lines

Layout (prefix + G)

|  70%   | 30% |   <- 75% height
|        |     |
|--------|-----|
|    100%      |   <- 25% height
|--------------|

Focus lands on the top-left (main) pane after creation.

Changes

• tmux.conf: Add bind-key G with resize-pane for accurate percentages
• tmux.conf: Add set -g history-limit 1000000
• cmd/deploy/main.go: Update tmux dest to ~/.config/tmux/tmux.conf
• deploy.sh: Update tmux path in backup, check, and deploy logic

Usage

Press Ctrl-a + G to create the 3-pane layout.