Add clear cache indicators to output

- Show "⚡ CACHED RESULTS (Xh old)" in compact output header
- Add "use --refresh for fresh data" hint
- Track from_cache and cache_age_hours in Report schema
- Update UI to show cache age in stderr message

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

scripts/lib/render.py

@@ -29,6 +29,13 @@ def render_compact(report: schema.Report, limit: int = 15) -> str:
     # Header
     lines.append(f"## Research Results: {report.topic}")
     lines.append("")
+
+    # Cache indicator
+    if report.from_cache:
+        age_str = f"{report.cache_age_hours:.1f}h old" if report.cache_age_hours else "cached"
+        lines.append(f"**⚡ CACHED RESULTS** ({age_str}) - use `--refresh` for fresh data")
+        lines.append("")
+
     lines.append(f"**Date Range:** {report.range_from} to {report.range_to}")
     lines.append(f"**Mode:** {report.mode}")
     if report.openai_model_used: