Add the ProtonVPN server networks and addresses to the IP lookup (closes #236)

Proton's own server list answers only a logged-in session, so the lists come from the public mirror https://github.com/tn3w/ProtonVPN-IPs, downloaded once a day: `protonvpn`, its /24 networks, and `protonvpn_entry`, its servers' IPv4 and IPv6 addresses. Both feed `flags.is_vpn` and `vpn_providers`.

Judgement call: the /24 networks are listed as well as the exact addresses, because coverage matters more than attribution, so neighbouring addresses in those networks count too.
Risk: the mirror is one person's repository; if it stops updating, downloads keep succeeding with old data.

Model: opus-5-5

TODO.md

@@ -53,6 +53,10 @@ problem the run finds.
 
 # Completed Steps
 
+- 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
+  https://git.eeqj.de/sneak/routewatch/issues/236).
 - 2026-11-10: the IP lookup finds PTR names over DNS-over-HTTPS and caches them
   for the record's TTL, in memory and in `cache.db` (closes
   https://git.eeqj.de/sneak/routewatch/issues/238).