tmux: add session wizard (switch or create via zoxide+fzf)

[connorads]

Why

Current tmux picker switches existing sessions well, but project-oriented workflows benefit from one flow that can switch to an existing session or create a new one from recent directories.

Scope

• Add a session wizard plugin/workflow (zoxide + fzf)
• Keep existing session picker as fallback
• Choose non-conflicting keybind (likely Ctrl+b T)
• Ensure behaviour works in local and remote tmux usage

Acceptance criteria

• One key opens a popup listing sessions + project dirs
• Selecting existing session switches immediately
• Selecting dir creates/switches to appropriately named session
• Keybinding documented in ~/.config/tmux/help.md