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

TODO.md

@@ -35,6 +35,14 @@ tested.
 
 # Completed Steps
 
+- 2026-10-27: the home page has cards with figures of the routing table: 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 cards count the bogon announcements and the prefixes with more
+  than one origin AS, and link to the new pages `/bogons` and
+  `/multiple-origins` that list them. A new package, `internal/bogon`, tells
+  which prefixes and AS numbers are reserved. The server works the figures out
+  once a minute (closes #154)
 - 2026-10-27: the per-peer route tables are gone, with the code that wrote,
   counted and read them. The prefix handler applies each update to the routing
   table in memory and writes the table's changes every second. It also stores