itinerary: link Silicon Valley stops

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

sf_sights.md

@@ -35,9 +35,9 @@
 
 ## Silicon Valley (car, ~45 min south)
 
-- **Apple Park Visitor Center** — Cupertino; rooftop view of the ring, AR model, store. Campus itself is closed to the public
-- **Google Visitor Experience** — Mountain View; store, café, Android statues
-- **Computer History Museum** — Mountain View; Wed–Sun 10 AM–5 PM, closed Mon–Tue. Fits Sun Sep 20 only
+- **[Apple Park Visitor Center](https://www.apple.com/retail/appleparkvisitorcenter/)** — Cupertino; rooftop view of the ring, AR model, store. Campus itself is closed to the public
+- **[Google Visitor Experience](https://visit.withgoogle.com/plan-your-visit/)** — Mountain View; store, café, Android statues
+- **[Computer History Museum](https://computerhistory.org/hours-admission/)** — Mountain View; Wed–Sun 10 AM–5 PM, closed Mon–Tue. Fits Sun Sep 20 only
 - **Stanford campus** — Palo Alto; Hoover Tower view
 
 ## Mission / Castro