feat: built-in copy Action copies the Project path (ctrl+y) #66

Part of #61.

What

A built-in copy Action, bound to ctrl+y, that copies the Project's absolute path to the clipboard. It is detached, so the Picker stays open, and the footer briefly says "copied".

• Uses wl-copy (when WAYLAND_DISPLAY is set), then xclip -selection clipboard, then xsel --clipboard, then pbcopy, whichever is found first.
• If none is found, falls back to the OSC 52 escape written to /dev/tty, which also works over SSH in terminals that allow it.

Acceptance

• The tool selection order is tested with a fake PATH.
• The OSC 52 sequence is tested byte-for-byte.