itinerary: drop Alcatraz sold-out warning

Claude-Session: https://claude.ai/code/session_01SQPbfX7jyTALGYxJw36hbT

days/2026-09-21.md

@@ -16,5 +16,5 @@
 ## Notes
 
 - Silicon Valley and the Golden Gate sunset moved to [Sep 20](2026-09-20.md)
-- **Alcatraz** — ferry from Pier 33, ~2.5–3 hrs, no car needed. Sells out weeks ahead — reserve early if wanted
+- **Alcatraz** — ferry from Pier 33, ~2.5–3 hrs, no car needed. Tickets: [alcatrazcitycruises.com](https://www.alcatrazcitycruises.com/)
 - **Monday:** some museums (incl. the de Young, Computer History Museum) are closed