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>

app/globals.css

@@ -14,6 +14,11 @@
   --color-open-text: #4ade80;
   --color-open-hours: #bbf7d0;
 
+  --color-ph-bg: #1e0f2e;
+  --color-ph-border: #7e22ce;
+  --color-ph-hours: #e9d5ff;
+  --color-ph-label: #c084fc;
+
   --color-today-bg: #0c1a3d;
   --color-today-border: #2563eb;
   --color-today-text: #93c5fd;