Add $FZF_COMPLETION_TMUX_LEGACY for Flexible tmux Integration

[stonematt]

This update introduces the $FZF_COMPLETION_TMUX_LEGACY environment variable, giving users the flexibility to switch between the legacy fzf-tmux wrapper and the modern fzf --tmux integration. By default, $FZF_COMPLETION_TMUX_LEGACY is set to true, preserving the current behavior. When set to false, it leverages native fzf --tmux, fixing command interpretation issues like:

bash: fzf-tmux --height=40% -- : command not found

The README has been updated with instructions for using the new environment variable and includes a tip on enabling fzf’s tmux mode (export FZF_TMUX=1) for smoother completion experiences, as suggested in the fzf README.

Key Changes:

• Enhanced fzf_bash_completion_selector to switch between legacy and native tmux handling based on $FZF_COMPLETION_TMUX_LEGACY.
• Updated the README to include the new variable and a tip for enabling tmux mode with fzf.

Why This Change:

This fixes known issues with legacy fzf-tmux command interpretation while allowing users to switch to the more robust native fzf --tmux integration for enhanced reliability.

Testing:

• Verified both legacy and native tmux modes work as expected in bash with and without tmux.
• Confirmed proper fallback behavior in case of missing configurations.