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>

goodnews/db.py

@@ -19,6 +19,12 @@ CREATE TABLE IF NOT EXISTS sources (
     active INTEGER NOT NULL DEFAULT 1,
     poll_interval_minutes INTEGER NOT NULL DEFAULT 60,
     notes TEXT,
+    last_success_at TEXT,
+    last_error_at TEXT,
+    last_error TEXT,
+    consecutive_failures INTEGER NOT NULL DEFAULT 0,
+    review_flag INTEGER NOT NULL DEFAULT 0,
+    review_reason TEXT,
     created_at TEXT NOT NULL DEFAULT CURRENT_TIMESTAMP,
     updated_at TEXT NOT NULL DEFAULT CURRENT_TIMESTAMP
 );
@@ -148,3 +154,16 @@ def _migrate(conn: sqlite3.Connection) -> None:
         )
     # Created here (not in SCHEMA) so it runs after the column exists on upgrades.
     conn.execute("CREATE INDEX IF NOT EXISTS idx_articles_duplicate_of ON articles(duplicate_of)")
+
+    source_cols = {row["name"] for row in conn.execute("PRAGMA table_info(sources)")}
+    health_columns = {
+        "last_success_at": "TEXT",
+        "last_error_at": "TEXT",
+        "last_error": "TEXT",
+        "consecutive_failures": "INTEGER NOT NULL DEFAULT 0",
+        "review_flag": "INTEGER NOT NULL DEFAULT 0",
+        "review_reason": "TEXT",
+    }
+    for column, decl in health_columns.items():
+        if column not in source_cols:
+            conn.execute(f"ALTER TABLE sources ADD COLUMN {column} {decl}")