Move guidance about pty-blocking commands from the `TerminalToolInput`
struct-level doc comment to the `command` field's doc comment so it's
surfaced more prominently to the model in the tool's JSON schema, and
call out `--no-pager` and `GIT_EDITOR=true` explicitly for git
operations.

In practice, the previous wording about `git --no-pager diff` was easy
for agents to overlook, leading to terminal calls that block waiting on
`less` (for `git log`/`git diff`/`git show`) or on an interactive editor
(for `git rebase`/`git commit`/`git merge`).

Unit eval change before/after wording change:

<img width="1662" height="740" alt="image"
src="https://github.com/user-attachments/assets/5f7921f3-87fa-4f88-9839-193ca4522572"
/>

Closes AI-154

Release Notes:

- Zed Agent's terminal tool now much more consistently uses `--no-pager`
and `GIT_EDITOR` with `git` commands