Remove passed June 18 event CTA from one-pager hero

[Alysha from Motion (alyshafrommotion)]

Removes the hero CTA anchor ("🚀 Tune in June 18 at 1pm ET to see Runneth live") and its now-unused .hero-event styles from use-case-library-site/server/src/one-pager.html. The June 18 event has passed.

Requested by Rabia, greenlit by Faye (admin). One-block delete, no other changes.

Merge path: staging first (Giselle), then staging → main (Vamsi) for the Railway prod deploy.

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge.

The HTML element and its dedicated styles are removed together, with no remaining behavior or references affected.

_{Reviews (1): Last reviewed commit: "Remove passed June 18 event CTA from one..." | Re-trigger Greptile}