feat: add Punishing: Gray Raven with karendar.com source

Add karendar.com as the event source for Punishing: Gray Raven (PGR).
Karendar publishes a dedicated Global event calendar with exact UTC
timestamps in clean server-rendered HTML.

- Register 'pgr' in GameId and GAMES registry (#CC292B, Kuro Games).
- Add parseWeekdayDayMonthYearUtc in src/ingest/dates.ts with unit tests.
- Implement karendarParser in src/ingest/parsers/karendar.ts reading
  'week', 'ongoing', and 'upcoming' sections, mapping indefinite/permanent
  ends to endsAt: null, and categorizing tags to EventType.
- Register pgr-karendar-events in src/ingest/adapters/index.ts.
- Add pinned fixture, expected output, and comprehensive test suites.
- Update documentation in AGENTS.md, README.md, docs/INGESTION.md,
  and docs/SOURCES.md.

test/adapters/game8.test.ts

@@ -64,6 +64,8 @@ const CASES: Array<{ adapter: Adapter; fixture: string }> = [
   // edge the source labels `ESTIMATED WEEK`, not an announced date — see
   // src/ingest/parsers/arustats.ts and docs/SOURCES.md § 14.
   { adapter: adapter("hi3-arustats-events"), fixture: "fixtures/hi3/arustats-events-2026-08-27" },
+  // Punishing: Gray Raven (karendar.com). Exact UTC timestamps for the Global server.
+  { adapter: adapter("pgr-karendar-events"), fixture: "fixtures/pgr/karendar-events-2026-09-12" },
 ];
 
 async function runAdapter(adapter: Adapter, fixture: string) {