news: reduce headline max age from 24h to 12h, make configurable

- Added headline_max_age_seconds to NewsConfig (default 43200 = 12h)
- Replaced hardcoded 86400 in _fetch_news_sentiment_raw with config ref
- All downstream consumers (keyword scoring, LLM scoring, LLM summary,
  agent panel macro/contrarian) auto-filter through the same path

news_engine.py

@@ -770,8 +770,8 @@ class NewsEngine:
                         pub_date_el.text if pub_date_el is not None else None
                     )
 
-                    # Only recent headlines (last 24h)
-                    if pub_date and (datetime.now(timezone.utc) - pub_date).total_seconds() > 86400:
+                    # Only recent headlines (configurable: headline_max_age_seconds)
+                    if pub_date and (datetime.now(timezone.utc) - pub_date).total_seconds() > self.config.headline_max_age_seconds:
                         continue
 
                     # Dedup within and across feeds so a syndicated story