fix: stop failing the build on a page that says it has no events

Infinity Nikki's wiki prints "There are no Events in this category"
between versions, and the refresh runner has honoured that since
2026-09-03 — it stores the empty parse as the source's real answer
rather than letting a quiet lane reach the broken tier. The feed build
never asked, so the same page arrived at CI as parsedCount 0,
indistinguishable from a parser that has stopped reading a redesigned
page, and brokenSources failed every build while every refresh stayed
green.

The runner's verdict cannot travel on its own: only a parser has seen
the page, and by the time brokenSources runs there is nothing left but
the feed. So the fact rides on SourceHealth, defaulted so an older feed
the service worker cached keeps validating and reads as the strict
answer.

Both ends now ask it the same way — of an empty parse only, from the
page's own words only — because a redesign yields zero rows too, and
excusing that is the silently emptied calendar the gate exists for.

The rule sits in a module rather than in build-feed.ts, which writes
public/ and so runs a build if a test imports it. That is how the two
ends drifted apart with nothing to catch it.

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

test/custom-ui.test.tsx

@@ -240,6 +240,7 @@ describe("Colophon freshness notice (PRD F7)", () => {
     eventCount: 9,
 
     parsedCount: 9,
+    statesNoEvents: false,
   };
 
   test("states when the data was refreshed, unprompted", () => {