feat: add Chaos Zero Nightmare, which the game8 parser already reads

No parser work at all — a GameId, a games entry, a SOURCES line, a fixture and
a test. The page lists six current events and the parser publishes four; the
two it skips print "Start Date: -", and no start means no event ID, so that is
the skip-never-guess rule working rather than a silent drop.

The cost is worth stating plainly: this is the ninth game8 source, and game8's
edge answers the Actions runner with a 202 and a bot-management body, so the
lane is built from a checked-in fixture in CI from day one and only a manual
`bun run refresh` moves it. freshness() discloses that in the footer, which is
what it is for.

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",
+  "ba", "fgo", "holodori", "gfl2", "stellasora", "czn",
 ]);
 
 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 and Blue Archive carry **no `resetOffsets`
+Infinity Nikki, P5X, Blue Archive and Chaos Zero Nightmare 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: