Unstick the backend issues with Landlord Mapper

Current problem

A backend/data layer and frontend exist, but the connection between them is incomplete. Hosting and administrative access appear fragile, and the current free-tier Supabase arrangement may become inactive after periods of disuse.

First step

Confirm the actual current architecture, repositories, service ownership, access, and remaining integration gap rather than relying on meeting summaries.

Goal

Produce the smallest showable Landlord Mapper flow: a user submits an address or query, the deployed application reaches the backend/data source, and relevant results are displayed.

Definition of done

• Current architecture and ownership confirmed.
• Required contributors have an appropriate access pathway.
• Frontend/backend integration works in a deployed environment.
• Runtime ownership does not depend solely on an undocumented personal account.
• Setup and handoff information are documented.
• Lessons and policy decisions are fed into #510.

Related: #505 and #484.