feat: add Umamusume, from Game8's banner list

uma.moe stays declined — its API sits behind a Cloudflare Turnstile proof
header, and an adapter would mean defeating a deliberate access control. This
is the surface that is simply open, and it needed the parser change in the
commit before this one to be readable at all.

The stable URL matters: Game8 also publishes monthly "August 2026 Release
Schedule" pages whose id changes every month, which a static registry cannot
follow. "List of All Banners" does not move.

Four current banners, both columns of the side-by-side table, and none of the
Previous Banners below them. The tenth game8 source, so it carries the same CI
blindness as the other nine and only a manual refresh moves it.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

docs/DATA-MODEL.md

@@ -10,7 +10,7 @@ import { z } from "zod";
 
 export const GameId = z.enum([
   "genshin", "hsr", "zzz", "wuwa", "arknights", "endfield", "nte", "nikki", "p5x", "r1999",
-  "ba", "fgo", "holodori", "gfl2", "stellasora", "czn",
+  "ba", "fgo", "holodori", "gfl2", "stellasora", "czn", "uma",
 ]);
 
 export const EventType = z.enum([
@@ -308,7 +308,7 @@ nothing to add, which is the point worth carrying to the next game: an override
 the game moves nobody, while the same override added a year later re-labels every tick already
 logged under the old clock. Get it right at introduction or accept a migration.
 
-Infinity Nikki, P5X, Blue Archive and Chaos Zero Nightmare carry **no `resetOffsets`
+Infinity Nikki, P5X, Blue Archive, Chaos Zero Nightmare and Umamusume carry **no `resetOffsets`
 entry**, so they take the regional default. That is an assumption, not a verified server map — none
 of those sources states one. Two of the 2026-08-19 additions are worth separating out, because they
 are silent for different reasons and neither is the usual one: