v0.9.5 - implement overlay: no selectable text, clipboard + primary

The paste was picking up the rendered box - the float border and the sidebar behind it - because the prompt was drawn as selectable text and a mouse drag (or copy-on-select) grabbed the whole rows and clobbered the clean clipboard.

Fixes:

• When the auto-copy succeeds, the overlay renders no prompt text at all - nothing to drag-select. It just says "✓ the implement instruction is on your clipboard. Press enter, then paste (Ctrl+Shift+V / middle-click)."
• Clipboard writes now set both the clipboard and the primary selection, so paste works whether you use Ctrl+Shift+V or middle-click.
• The prompt text is only shown as a manual fallback if no clipboard tool is reachable.

Just press enter and paste - no selecting.