Make cycle show classify progress and prevent overlapping runs

- cycle now prints per-article classify progress (flushed) so the long step is
  clearly alive rather than appearing hung.
- An exclusive flock guards the cycle so a manual run and the systemd timer (or
  two timer ticks) cannot overlap and contend on the database and model.

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

goodnews/llm.py

@@ -5,6 +5,7 @@ import os
 import sqlite3
 import urllib.error
 import urllib.request
+from collections.abc import Callable
 from dataclasses import dataclass
 
 from .taxonomy import (
@@ -226,12 +227,13 @@ def classify_articles(
     include_rejected: bool = False,
     dry_run: bool = False,
     only_unclassified: bool = False,
+    progress: "Callable[[int, int, int], None] | None" = None,
 ) -> list[tuple[int, dict]]:
     rows = _classification_candidates(
         conn, limit=limit, include_rejected=include_rejected, only_unclassified=only_unclassified
     )
     results = []
-    for row in rows:
+    for index, row in enumerate(rows, start=1):
         try:
             scores = client.classify(row)
         except RuntimeError as exc:
@@ -244,6 +246,8 @@ def classify_articles(
         if not dry_run:
             upsert_article_score(conn, row["id"], scores)
             conn.commit()
+        if progress is not None:
+            progress(index, len(rows), row["id"])
     return results