Center map on home and fit route bounds

[cafca]

Summary

• Home centering on load: Pre-loads session and home location before mounting the map, so the map initializes at the home coordinates with no visible jump
• Home centering on login: When a user logs in, the map instantly jumps to their home location
• Route fit bounds: When computing a route, the map smoothly pans and zooms to fit both origin and destination in view (400ms transition, extra vertical padding for UI elements)

Details

createMap() now accepts optional center/zoom params. App.svelte awaits checkSession() + loadHomeLocation() before rendering the <Map> component, passing the home coordinates through.

For route fitting, uses LngLatBounds.extend() instead of the two-argument constructor to avoid a MapLibre bug where SW longitude > NE longitude is interpreted as antimeridian wrapping, causing the map to zoom out to show the entire globe.

Test plan

• Load app while logged in with a home set — map should start centered on home, no flash/jump
• Log in from anonymous — map should jump to home
• Request a route — map should smoothly fit to show both endpoints
• Request a short route (~50m) — should stay zoomed in (maxZoom: 15)
• Route endpoints should not be hidden behind top/bottom UI