feat(admin-ui): sub-room caps and test-case issue linking

Two admin screens for work that previously had server support but no way to
reach it.

Rooms → a room → Sub-rooms: per-sub-room max players, with the room's own
advertised capacity shown alongside so the two are not mistaken for each other.
Each row also shows whether the sub-room is a matchmaking target and which blob
it loads.

Activity → Test cases: file a GitHub issue against a case, follow the link, or
unlink it, plus a reconcile button. Filing is idempotent server-side, so the
button is safe to press twice. When GitHub is unconfigured the actions disable
themselves and the page explains why rather than failing on click — a server
with no token is an ordinary deployment.

Both go in as tabs on the existing hub pages rather than new sidebar entries,
matching how the nav is organised.

Server side adds GET api/admin/v1/testcases (the list the SPA renders, with
each case's issue number) and mirrors the three issue routes under
/api/admin/v1/testcases/... because the SPA's client speaks that prefix
exclusively.

I had told the user this UI was not possible on this branch because
wwwroot/admin holds a built bundle. That was wrong — the source is in
DorkNet.Server/admin-ui and builds to it.

docs/admin.md

@@ -56,7 +56,7 @@ that outer check.
 |---|---|---|
 | Overview | `/` | Live ops dashboard, online players, active sessions, quick kick/ban/broadcast actions |
 | Moderation | `/players` | Player directory, bans, reports, per-player ban/grant/gift/password/avatar/account actions |
-| Activity | `/activity` | Admin audit log and per-player request logs |
+| Activity | `/activity` | Admin audit log, per-player request logs, QA test cases + GitHub issue linking |
 | Content | `/rooms`, `/rooms/:id`, `/import-room`, `/content` | Room list/detail, room import, instances, leaderboards, community board, loading tips, 3D Charades word lists |
 | Operations | `/broadcast`, `/settings` | Server broadcast, server toggles (signups, everyone-is-friends, profanity filter, imported-room version clamp), signup codes, weekly challenges, Play menu tags, Rec Center doors, game config values |
 
@@ -193,6 +193,12 @@ QA test cases can file and track GitHub issues. Configure with:
 endpoints answer `503` with the reason, and the background reconciler logs once
 and idles. A server with no GitHub credentials is a normal deployment.
 
+UI: **Activity → Test cases** (`/activity?tab=testcases`). File or unlink an
+issue per case, or reconcile them all. The buttons disable themselves with an
+explanation when GitHub is unconfigured rather than failing on click.
+
+Sub-room caps live on the room page: **Rooms → a room → Sub-rooms**.
+
 Endpoints (admin-gated — these are not part of the 2023 client's surface):
 
 - `POST api/testcasemanagement/v1/testcase/{id}/issue` — file and link.
@@ -206,6 +212,11 @@ Endpoints (admin-gated — these are not part of the 2023 client's surface):
 - `POST api/testcasemanagement/v1/issues/sync` — reconcile now. The background
   service runs the same code path on its interval, so manual and automatic
   cannot drift.
+- `GET api/admin/v1/testcases[?passId=&status=]` — the list the SPA renders,
+  with each case's issue number and link.
+
+Each of the three also answers under `/api/admin/v1/testcases/...`, because the
+admin SPA speaks that prefix exclusively.
 
 ### Where the link is stored