ci: make feedback backfills observable

[haasonsaas]

Summary

• add --progress logging to the feedback sweep so long backfills show which PR is being inspected
• enable progress logging in the 30-day backfill workflow
• reduce the scheduled/default backfill PR cap from 1000 to 250 after a live 1000-PR dispatch stayed in progress for several minutes

Verification

• ruby -c .github/scripts/sweep-recent-review-feedback.rb
• ruby -Itest test/sweep_recent_review_feedback_test.rb
• for file in test/*_test.rb; do ruby -Itest "$file" || exit 1; done
• actionlint .github/workflows/review-feedback-backfill.yml .github/workflows/review-feedback-sentinel.yml

Context

A full pr_limit=1000 30-day dispatch stayed in the sweep step long enough to look hung and had no per-PR progress output. I cancelled that run and made broad backfills observable before widening again.

[cursor]

PR Summary

Low Risk
Low risk: adds optional stderr progress logging and tweaks workflow defaults without changing the feedback detection/ledger semantics; main risk is slightly noisier CI logs and different backfill coverage due to the lower default PR limit.

Overview
Makes long-running review-feedback sweeps observable by adding a --progress / progress: option that prints PR-inspection progress to stderr (including total PRs scanned and the current repo#PR).

Updates the 30-day review-feedback-backfill.yml workflow to enable --progress and lowers the default pr_limit from 1000 to 250 to avoid overly long backfills. Adds a focused test asserting the new progress output.

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