itinerary: move Silicon Valley and Golden Gate sunset to Sep 20

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

itinerary.md

@@ -42,7 +42,7 @@ One file per day in [`days/`](days/): logistics, agreed plan, open notes.
 | Date | Day | Where |
 |---|---|---|
 | [Sep 19](days/2026-09-19.md) | Sat | Daly City |
-| [Sep 20](days/2026-09-20.md) | Sun | San Francisco |
+| [Sep 20](days/2026-09-20.md) | Sun | Silicon Valley · Golden Gate |
 | [Sep 21](days/2026-09-21.md) | Mon | San Francisco |
 | [Sep 22](days/2026-09-22.md) | Tue | SF → Yosemite |
 | [Sep 23](days/2026-09-23.md) | Wed | Yosemite |