Builds out the rest of the transit UX from data Transitous actually provides.
- Time picker: Leave now / Depart at / Arrive by (MOTIS time + arriveBy).
- Mode filter: Bus/Tram/Metro/Train/Ferry groups -> MOTIS transitModes.
- Stop departure boards: tap a stop name -> MOTIS stoptimes, with live and
cancelled badges and a feed-provided platform hint.
- Fares: MOTIS carries NO prices (verified live: debugOutput.fares=0,
agencyFareUrl empty), so a 'tickets' link is shown ONLY when the feed supplies
an operator fare URL - never an invented price.
New src/lib/transitUi.ts holds the mode vocabulary (emoji/colour/groups) so the
itinerary and the board cannot drift; StopDepartures.tsx is its own dialog.
Docs: AGENTS.md transit note.
