Add best-effort geolocation to the IP lookup from geojs and DB-IP City Lite (closes #239)

Each result gains `geo`. One request to geojs carries every address, 1 second in all. On a timeout, an error or an answer with no country, city or coordinates, the lookup reads DB-IP City Lite, downloaded monthly into the state directory. geojs answers stay in memory (250,000, least recently used dropped) and in a new `cache.db` table for 7 days.

Judgement call: a reserved address goes to neither source, and its `geo` is null.
Judgement call: `updated` for DB-IP is when the copy was downloaded.
Deviation: the cache is SQLite, by sneak's words.

Model: opus-5-5

TODO.md

@@ -53,6 +53,10 @@ problem the run finds.
 
 # Completed Steps
 
+- 2026-11-10: each result of the IP lookup has `geo`, where the address is. It
+  comes from geojs, with DB-IP's City Lite database as the fallback. The geojs
+  answers stay in memory and in `cache.db` for 7 days (closes
+  https://git.eeqj.de/sneak/routewatch/issues/239).
 - 2026-11-10: the IP lookup checks the `protonvpn` list of ProtonVPN's /24
   networks and the `protonvpn_entry` list of its servers' IPv4 and IPv6
   addresses, from a public mirror of Proton's server list (closes