Show figures of the routing table on the home page (closes #154)

The home page gets cards for the newest and oldest kept route, the newest
and oldest updated AS, the AS with the most prefixes, the ASes with a
single prefix and fifteen well-known networks. Two more cards count the
bogon announcements and the prefixes with several origin ASes. They link
to the new pages /bogons and /multiple-origins, which list up to 1,000
entries each.

The new package internal/bogon tells reserved prefixes and AS numbers,
from the IANA special-purpose registries. Table.Overview walks the table
and lets the read lock go every 10,000 prefixes. The server works the
cards out once a minute and serves that copy. A new index on
asns(last_seen) finds the newest and oldest updated AS.

Model: opus-5-5

internal/database/interface.go

@@ -62,6 +62,7 @@ type Store interface {
 
 	// AS and prefix detail operations
 	GetAS(ctx context.Context, asn int) (*ASN, bool, error)
+	GetLastSeenASes(ctx context.Context) (*ASN, *ASN, error)
 	GetASWHOIS(ctx context.Context, asn int) (*ASN, error)
 	GetPrefixFirstSeen(ctx context.Context, prefix netip.Prefix) (time.Time, error)
 	GetASPeers(asn int) ([]ASPeer, error)