Advisory source health: review flags, never auto-deactivate

- Add source health columns (last_success_at, last_error_at, last_error,
  consecutive_failures, review_flag, review_reason) via SCHEMA + migration.
- poll_source maintains them: success resets the failure streak and records the
  success time; failure increments it and stores the latest error.
- review_sources() flags active sources that are stale, repeatedly failing,
  low-acceptance, duplicate-heavy, or doom-skewed (high cortisol/ragebait) over
  a recent window. It is purely advisory: it sets review_flag/review_reason and
  never changes the active column (human stays in the loop), clearing the flag
  when a source recovers.
- CLI review-sources; cycle runs it as a final step (--no-review to skip);
  source-report shows a review line for flagged feeds.
- Tests: healthy/failing/stale/low-acceptance/recovery and never-deactivates.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -22,6 +22,7 @@ python3 -m goodnews suggest-source https://example.com/feed/ --name "Example" --
 python3 -m goodnews list-candidates
 python3 -m goodnews promote-candidate 1        # copies into sources (inactive by default)
 python3 -m goodnews reject-candidate 1
+python3 -m goodnews review-sources             # advisory health flags (never deactivates)
 python3 -m goodnews build-brief --date 2026-05-27 --replace
 python3 -m goodnews show-brief
 python3 -m goodnews list-recent --limit 10
@@ -161,7 +162,7 @@ often as you like — it only polls sources that are *due* (per each source's
 rebuilds the current day's brief:
 
 ```bash
-python3 -m goodnews cycle                 # poll due -> classify new -> dedup -> rebuild today's brief
+python3 -m goodnews cycle                 # poll due -> classify -> dedup -> brief -> review flags
 python3 -m goodnews cycle --force         # poll every active source regardless of interval
 python3 -m goodnews cycle --no-classify   # skip the LLM step (e.g. model box offline)
 ```
@@ -195,9 +196,11 @@ Still ahead:
    previews a feed and stages it in the `source_candidates` table (status
    suggested/quarantined/rejected/promoted); `promote-candidate` copies it into
    `sources` (inactive by default — active on approval); promotion is never
-   automatic. Still ahead: advisory auto-degrade of stale/rejecting feeds (flag
-   for review, never auto-block), and an authenticated POST surface so the website
-   can accept public suggestions once accounts exist.
+   automatic. Advisory health is done too: `review-sources` (also run at the end
+   of `cycle`) flags stale, failing, low-acceptance, duplicate-heavy, or
+   doom-skewed feeds for human review — it never deactivates anything. Still
+   ahead: an authenticated POST surface so the website can accept public
+   suggestions once accounts exist.
 2. **Learned "Less like this" weighting** — replace the interim flavor-pause with
    real preference down-ranking.
 3. **Corpus rebalancing** — add calm/feelgood sources (currently science-heavy).