feat: add postcode coordinates to volunteer list response for map view

[nadavosa]

Summary

The volunteer list endpoint (GET /volunteers) returns ApiVolunteerGetList which includes locations: OptionItem[] (district names) but no coordinates. The volunteer map tab needs lat/lon to place pins.

Proposed change

Add lat and lon (nullable) to ApiVolunteerGetList from volunteer.person.address.postcode.latitude/longitude.

If the volunteer has no address or postcode, return lat: null, lon: null — the map simply skips pinless volunteers.

Notes

• Postcode entity already has latitude and longitude columns
• The volunteer list query already joins person — needs to also join person.address.postcode
• SDK type ApiVolunteerGetList will need updating too (coordinate with SDK bump)
• Only expose coordinates, never the full street address, in the list response (GDPR minimisation)

Depends on

Nothing — standalone BE change.