itinerary: split day plans into days/, plan SF Sep 21

- One file per day under days/; timeline table reduced to date, weekday, place
- Sep 19–20: KT & VT Uber to Airbnb, rest day; LK & MS drive rental to Airbnb
- Sep 21: Silicon Valley morning, optional Twin Peaks / Painted Ladies /
  Lands End, Battery Spencer at sunset
- LK Hertz LAX rental marked not available for planning; LA / San Diego
  hotels cancelled
- sf_sights: add Silicon Valley and Mission / Castro, skip Computer History
  Museum

Claude-Session: https://claude.ai/code/session_01CWLR7htYGAB9i89P8jCCLn

days/2026-09-28.md

@@ -0,0 +1,9 @@
+# Sep 28 (Mon) — Los Angeles
+
+**Stay:** [Airbnb — DTLA](../bookings/stays/airbnb-la-dtla.md)
+
+## Plan
+
+> Menu: [`la_sights.md`](../la_sights.md)
+
+- TBD