Add WHOIS stats to status page with adaptive fetcher improvements

- Add WHOIS Fetcher card showing fresh/stale/never-fetched ASN counts
- Display hourly success/error counts and current fetch interval
- Increase max WHOIS rate to 1/sec (down from 10 sec minimum)
- Select random stale ASN instead of oldest for better distribution
- Add index on whois_updated_at for query performance
- Track success/error timestamps for hourly stats
- Add GetWHOISStats database method for freshness statistics

internal/database/schema.sql

@@ -90,6 +90,7 @@ CREATE INDEX IF NOT EXISTS idx_peerings_lookup ON peerings(as_a, as_b);
 
 -- Indexes for asns table
 CREATE INDEX IF NOT EXISTS idx_asns_asn ON asns(asn);
+CREATE INDEX IF NOT EXISTS idx_asns_whois_updated_at ON asns(whois_updated_at);
 
 -- Indexes for bgp_peers table
 CREATE INDEX IF NOT EXISTS idx_bgp_peers_asn ON bgp_peers(peer_asn);