Where a server is, on the public instance API

/api/privapub/v1/instances/:host gains `geo`, the public projection of a
server's place already decided for public server locations
(PublicGeo.Project): city, coordinates and network for servers reporting
at least 10 users and not behind a CDN, the country otherwise, the CDN's
name for a CDN-fronted one, with DB-IP's attribution. `?host[]=`
answers up to 40 servers at once, and this server describes itself:
its host's address located once a day (SelfLocation), or
Statistics:Geo:Self when the owner sets it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

docs/ROADMAP.md

@@ -202,6 +202,7 @@ and circles (see Owner decisions).
 | Question | Decision |
 |---|---|
 | Sign-in | **One login.** decePubClient signs in on `/clientapi` and exchanges that JWT for one persona's Mastodon token (RFC 8693 token exchange on `/oauth/token`, `PersonaExchange`), one token per persona it uses. Only the seeded first-party application may exchange; the token names the persona, never the root, like any other. |
+| Server locations on the instance API | **Public, as the projection already decided for public server locations** (2026-10-03): city, coordinates to 0.1° and network only for servers reporting at least 10 users and not behind a CDN, the country otherwise, the CDN's name for a CDN-fronted one, with DB-IP's attribution. decePubClient's globe draws posts at their author's server. This server's own place comes from its host's address, or from `Statistics:Geo:Self` when the owner sets it (a server behind a proxy). |
 
 ## Libraries (researched; no maintained .NET ActivityPub library exists, so Letterbook and Iceshrimp.NET both wrote their own)