[W5] Test architecture and external-service reliability

[Claudio9701]

Outcome

PR failures indicate regressions while scheduled contracts detect upstream service drift.

Parent tasks

• separate unit, contract, integration, Docker, and live tests
• replace Nominatim, HDX, OSMnx/Overpass, ORS, Google, Geofabrik, and OSRM PR calls with fixtures/fakes
• add shared HTTP identification, timeout, retry, caching, and error policy
• add scheduled provider-friendly live contracts and coverage ratchet

Acceptance

Unit tests cannot access the network and public-service use follows provider policy.

Plan: PR #61