Builds on @Hardik-369's instance-specific User-Agent idea and reworks the rest
of the #1309 fix:
- keep the unique User-Agent (buildUserAgent) — a shared UA gets the public
Overpass mirrors to rate-limit harder; it appends the configured instance
URL and is applied to every Nominatim/Overpass/Wikimedia call
- add OVERPASS_URL so an operator behind locked-down egress (e.g. a Kubernetes
cluster) can point the explore search at an internal/self-hosted Overpass
instance instead of the public mirrors
- keep the per-endpoint timeout default at 12s but make it tunable via
OVERPASS_TIMEOUT_MS for slow self-hosted instances; non-positive/invalid
values fall back to the default rather than 502-ing every search at a 0ms cap
- log each endpoint's failure reason before the 502 so blocked egress is
diagnosable instead of a bare "Overpass request failed"
Adds unit tests for the User-Agent, endpoint and timeout resolution plus the
all-mirrors-down path, and documents the two new env vars in .env.example, the
wiki and the Helm chart.
005e0c109d