Remove the round cap from the Copilot review loop; add the scope-creep caution #4931

Problem

The Copilot review loop in this repo has a fourth exit that the MCP Inspector's does not: a timeout after "about ten rounds".

• AGENTS.md, Issue-driven work style: "…or a timeout (the loop's budget is spent while findings keep coming)."
• .claude/skills/pr-flow/SKILL.md, step 9: "Timeout: The loop's overall budget is spent: about ten rounds, or the session is ending, while findings keep coming. Stop, and list what is still open in the summary so a human can pick it up."

Both arrived with the pr-flow skill (#4867). The Inspector's loop has three exits (the first clean round, a round of only out-of-scope findings, two rounds in a row that end without a review) and no round cap.

A cap stops a loop on a count rather than on a reason. On #4928 the loop reached round nine with every finding still a real defect in code the PR added; stopping at ten would have left a PR with known open findings and nothing but a number to explain why.

What actually ends a long loop is the scope rule, and the Inspector says so where it matters: "Copilot does not converge on its own, and every fix it talks you into beyond the issue is fresh surface for the next round, so accepting scope creep is what makes a review cycle protracted." This repo has the scope rule under Responding to code reviews, but not that warning next to the loop.

Expected

• The loop has the Inspector's three exits and no round cap, in both AGENTS.md and the pr-flow skill.
• AGENTS.md carries the caution beside the loop rule: Copilot does not converge on its own, so each finding is weighed against the issue the PR closes and scope expansion is declined.
• The skill says what to do when a session has to end mid-loop (report the round as pending), since that was the one useful part of the removed exit.

Decided by a maintainer in the session that opened #4927 and #4928.