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/server/server.go

@@ -13,9 +13,18 @@ import (
 	"github.com/go-chi/chi/v5"
 )
 
+// ASNFetcherStats contains WHOIS fetcher statistics.
+type ASNFetcherStats struct {
+	SuccessesLastHour int
+	ErrorsLastHour    int
+	CurrentInterval   time.Duration
+	ConsecutiveFails  int
+}
+
 // ASNFetcher is an interface for queuing ASN WHOIS lookups.
 type ASNFetcher interface {
 	QueueImmediate(asn int)
+	GetStats() ASNFetcherStats
 }
 
 // Server provides HTTP endpoints for status monitoring