Cache: add get_stale() for last-known-good fallback when APIs fail.
Fetcher: on API failure or tripped circuit breaker, serve stale cached
data instead of returning None — dashboards never go blank after first
successful fetch. Add per-source rate limits (11 sources configured).
Fix Yahoo Finance: compute change_pct from previousClose when
regularMarketChangePercent is absent (Yahoo v8 API change).
Fix health RSS: replace dead WHO DON/ProMED/CIDRAP URLs with working
WHO news, CDC outbreaks, and Outbreak News Today feeds.
Fix wildfires: extend FIRMS query from 1-day to 2-day (NRT data lag),
include nominal-confidence fires (was filtering to high-only).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>