The single-source Nonlogs path hard-broke when Nonlogs went down. Read the
unified neroswap price Worker first (multi-exchange, volume-weighted, excludes
a dead source), with the direct nonlogs+kraken / cexswap+kraken paths as
fallbacks. RATE_PROVIDER now defaults to "unified"; nonlogs|cexswap force a
legacy single source first for debugging. Worker URL overridable via
UNIFIED_WOW_URL.