feat: detect passholder preview days and filter plain buyouts

- Buyout days are now treated as closed unless they carry a Passholder
  Preview event, in which case they surface as a distinct purple cell
  in the UI showing "Passholder" + hours
- DB gains a special_type column (auto-migrated on next startup)
- scrape.ts threads specialType through to upsertDay
- debug.ts now shows events, isBuyout, isPassholderPreview, and
  specialType in the parsed result section

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/scrape.ts

@@ -65,7 +65,7 @@ async function main() {
       try {
         const days = await scrapeMonth(apiId, YEAR, month);
         db.transaction(() => {
-          for (const d of days) upsertDay(db, park.id, d.date, d.isOpen, d.hoursLabel);
+          for (const d of days) upsertDay(db, park.id, d.date, d.isOpen, d.hoursLabel, d.specialType);
         })();
         openDays += days.filter((d) => d.isOpen).length;
         fetched++;