Widgets: in-app widget surface (news, markets, bike-share, transit) #68

Part of #67 — Widgets, location and weather

• Fetch and render the four widget feeds.
• Confirm which require authentication and which are public, and confirm the response shapes live
  — none of them are modelled in the app today.
• Transit needs the user's location for GET /api/widgets/transit/stops.

Tests: parse each feed; graceful empty/error states (a dead third-party feed must not break
the screen).

Filed from the parity review of feature/parity-wip @ 14d7795 against interlinedlist.com (OpenAPI /api/openapi.json, 233 paths) and the public help centre.