fix(geo): read the Nominatim override the way the schema validates it

Follow-up to #2379.

NOMINATIM_URL arrives from a compose file or a ConfigMap with whatever
whitespace was typed around it. The schema validates the trimmed string and
calls a blank one unset, the derivation did neither, so " " passed startup as
"use the default" and then became the base URL that cannot be fetched, and a
padded value lost every geocoding call the same way. It trims now, which is
also what the places client next door does with its own override.

The chart could not pass the variable at all: the ConfigMap is an allowlist and
an unknown key is dropped without a word, which is exactly the locked-down
cluster the override exists for.

The docs said what to set and not what it costs. They now say that it replaces
the public service with no fallback, that the endpoint has to speak the
Nominatim API, and that the one-per-second spacing stays either way, so nobody
stands up their own instance expecting it to run faster.

Test IDs follow the file again.

charts/trek/templates/configmap.yaml

@@ -73,6 +73,9 @@ data:
   {{- if .Values.env.MCP_RATE_LIMIT }}
   MCP_RATE_LIMIT: {{ .Values.env.MCP_RATE_LIMIT | quote }}
   {{- end }}
+  {{- if .Values.env.NOMINATIM_URL }}
+  NOMINATIM_URL: {{ .Values.env.NOMINATIM_URL | quote }}
+  {{- end }}
   {{- if .Values.env.OVERPASS_URL }}
   OVERPASS_URL: {{ .Values.env.OVERPASS_URL | quote }}
   {{- end }}

charts/trek/values.yaml

@@ -78,6 +78,11 @@ env:
   # Max MCP API requests per user per minute. Defaults to 300.
   # MCP_MAX_SESSION_PER_USER: "20"
   # Max concurrent MCP sessions per user. Defaults to 20.
+  # NOMINATIM_URL: ""
+  # Custom Nominatim base URL for every geocoding call the server makes (place search, reverse lookup, Atlas region
+  # fill). When set it REPLACES the public OpenStreetMap service, with no fallback, so the instance behind it needs
+  # the coverage you expect and has to speak the Nominatim API. TREK keeps its ~1 request per second spacing either
+  # way. Defaults to https://nominatim.openstreetmap.org.
   # OVERPASS_URL: ""
   # Custom Overpass endpoint(s) for the map POI "explore" search, comma-separated. When set, REPLACES the bundled
   # public mirrors — point it at an internal/self-hosted Overpass instance when the public mirrors are unreachable