CDN-fronted servers grouped per CDN, and servers through time

A post whose server is behind a CDN has no place of its own: the globe
groups such posts per CDN in labels on a ring above the Arctic, and
hovering one draws its arc to the CDN's group and a ring where the
server was before the CDN. The card's CDN chip names the CDN, its
domain, how PrivaPub found it (published ranges, response headers or
network), the place before the CDN and the CDN's servers week by week
(/api/privapub/v1/cdns/:domain); the author's tooltip lists the server's
changes of place and CDN week by week (/instances/:host/history). Both
are read on the first hover and kept for the session.

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

CLAUDE.md

@@ -189,19 +189,24 @@ supplies:
   `PrivaPub.ClientModels`.
 - **Where a post is** (`InstanceService.Locate`, `Models/FeedPost.cs`): its own place (Pixelfed's, `privapub.place`),
   its event's venue, the reader for a located post, its author's server (to 0.1°, or a point in its country from
-  `Helpers/CountryPoints.cs` when DB-IP located it only to a country), or nowhere (a CDN-fronted server).
-  Server descriptions are cached a day in localStorage (`ServerInfos`). PrivaPub's own host is the signed-in persona's
-  account host, since the API may be reached under another name.
+  `Helpers/CountryPoints.cs` when DB-IP located it only to a country), or, for a CDN-fronted server, its CDN's group
+  (`LocationSource.Cdn`: no point, a `CdnKey` and the place `Before` the CDN). Server descriptions are cached a day in
+  localStorage (`ServerInfos`); a server's weekly history (`/instances/:host/history`) and a CDN's page (`/cdns/:key`)
+  are read on the first hover and kept for the session. PrivaPub's own host is the signed-in persona's account host,
+  since the API may be reached under another name.
 - **The feed page** (`Pages/Index.razor`): `FeedTabs`, `Content` (the card, which does its own actions), `Composer`,
   `GlobePanel`. Older pages load as the end comes near (`wwwroot/js/feed.js`); newer ones are polled every 45 s while
   the page is visible (PrivaPub has no streaming) and wait behind a "new" button.
 - **The globe** (`wwwroot/js/globe.js`, an ES module imported by `GlobePanel`) runs on globe.gl, vendored in
   `wwwroot/vendor/globe/` with its textures (`SOURCES.md` has versions, licences and hashes; the service worker never
   precaches it). It looks at the spherical mean of the located posts in view, pulses and draws an arc to a hovered
-  post, follows the theme (day/night texture), honours `prefers-reduced-motion` and pauses while hidden. The posts'
+  post, follows the theme (day/night texture), honours `prefers-reduced-motion` and pauses while hidden. CDN-fronted
+  posts are labels per CDN on a ring at 68°N, never a place; hovering one draws its arc there and a ring where the server
+  was before the CDN. The posts'
   places reach it in one call per feed change; cards are matched by `data-post-id`.
 - **Nerd stats** (`Components/Nerd/NerdTip.razor`, rows from `NerdRow`): a post's ids, times and provenance (read on
-  hover), its author and server, its place, media and counts; the feed's paging and last request; the globe's camera,
+  hover), its author and server with the server's changes of place and CDN week by week, its place or its CDN (how
+  PrivaPub found it, the place before it, the CDN's servers week by week), media and counts; the feed's paging and last request; the globe's camera,
   points and frame rate.
 
 **Localization (`Services/CoalescingStringLocalizer.cs`).**