fix(ui): slide the track and use a wide cover

[CodeDotJS]

Summary

• Slide the empty-ride track with a CSS animation so it moves on a phone.
• Start text size at the minimum. A larger size stays only after the slider is moved.
• Replace the tall share image with a wide print of The Great Wave off Kanagawa.

Test plan

• On a phone-width window, clear the route and confirm the track slides under the train
• Open Help and confirm the text-size slider starts at the left end
• Confirm /, /map, /city, and /help load on the preview