Follow up to https://github.com/zed-industries/zed/pull/47637

- Removes the requirement for the terminal to be focused to use the
`cmd->` keybinding. This way, we match the behavior of buffer selections
and you can always add what's selected in the terminal inside the agent
panel
- Add number of lines selected in the mention button as well
- Make the "Selection" menu item inside the "Add Context" menu also
observe terminal selections

<img width="420" height="254" alt="Screenshot 2026-01-29 at 1  36@2x"
src="https://github.com/user-attachments/assets/25d2eb00-096f-44d9-8882-273932ca43e4"
/>

Release Notes:

- Agent: Add number of liners selected in the terminal context mention