fix(cli): preserve chat -q answer by gating exit-summary screen clear (#60926)

[HEBEI77]

Fixes #60926 where running immediately erased the output because unconditionally cleared the terminal.

• Modified to accept argument.
• Gate the clear command in single-query mode.
• Updated in regression tests to match the new signature.

[alt-glitch]

This was generated by AI during triage.

Duplicate of #60926 — the maintainer salvage that gated _print_exit_summary's exit-clear behind a clear_screen kwarg (passing False on the chat -q path) was merged and is already on main (commit 58e1647). This PR re-implements the identical fix. Note it also bundles a leftover create_pr.sh artifact (whose body clones #60926's description) that shouldn't ship. Superseded by the merged #60926; related lineage #53025 (predecessor), #53009 (original issue).