review-loop: add Lite variant

[mattmoran56]

Summary

• Adds Lite variant of the review loop alongside the existing Pro pipeline. Lite is now the default.
• Lite per round: claude --print with /review <PR#> (or /review + diff) → fresh claude --print that embeds the review output and asks for sub-agent investigation + a markdown table → claude --print --resume <session_id> with "do what you think needs doing, commit, and push". No JSON intermediates, no sticky PR comment.
• Convergence: HEAD unchanged for a round = clean; N consecutive cleans → stop.
• Safety net: if the worktree is dirty after the fix turn, a trailing review-loop: trailing changes commit + push is made.
• UI: settings gets a Lite/Pro toggle; the panel branches on state.variant so Lite shows only the raw session transcript per round.

Screenshots

⚠️ Required before merge — PR touches UI (settings toggle + panel layout). Please attach a screenshot of the new Lite/Pro toggle in Settings → Review Loop and the Lite-mode panel in mid-run before merging.

Test plan

• Settings → Review Loop: Lite/Pro toggle renders, Pro button is not cut off
• Start review loop with variant=Lite on a branch with an open PR → /review <PR#> runs, transcript streams
• Start review loop with variant=Lite on a branch with no PR → falls back to inline diff in the prompt
• Triage phase emits a markdown table and makes no code changes; fix phase resumes the same session
• Trailing-commit safety net fires when fix leaves the worktree dirty
• Variant=Pro still behaves exactly as before (pipeline, issue rows, sticky PR comment)

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