feat(nvim): add git worktree picker that follows open buffers

Adds a telescope picker over 'git worktree list --porcelain'. Selecting an
entry cds to that worktree and re-points every open buffer at the same
relative path there, keeping cursor position and refusing to clobber
unsaved work.

Signed-off-by: unkin-agent <unkin-agent@unkin.net>

.config/nvim/lua/func.lua

@@ -6,6 +6,7 @@ require('func.tabline')
 require('func.popterm')
 require('func.sessions')
 require('func.findfile')
+require('func.worktree')
 
 --  vim.cmd [[
 --    augroup lang_all