Pico Transit v0.2.0

Adds a dedicated onboarding step and reworks the home screen:

• First launch (or switching agencies from Settings) now opens a welcome screen to pick your transit agency, instead of the home screen doubling as an always-visible picker
• Once an agency's picked, the home screen shows a ticking clock in its own timezone, the agency's name, and a loading indicator until the schedule's ready
• The clock stays visible while a trip is boarded too, alongside the live ETA and progress bar
• Settings' old default-agency toggle list is replaced with a single row that reopens the same picker to switch agencies

See RELEASE_NOTES.md for the full picture of everything unique to Pico Transit.