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

config.py

@@ -166,6 +166,9 @@ class NewsConfig:
     # Must stay below pre_event_buffer_minutes so an event can't cross
     # into the danger window while a stale cache says it's clear.
     context_cache_ttl_seconds: int = 600
+    # Maximum age of RSS headlines accepted for scoring. Older headlines
+    # are discarded before keyword analysis and LLM enrichment.
+    headline_max_age_seconds: int = 43200  # 12 hours
 
     rss_feeds: List[str] = field(default_factory=lambda: [
         "https://investinglive.com/feed/",