feat: add LocationService.create method

[2ndalpha]

Summary

• Add LocationService.create() method that calls POST /locations (V2 API) to create a new location
• New LocationCreationRequest interface with required fields (name, latitude, longitude, address, country) and optional fields (openingHours, inputFields, languages)
• New LocationCreatedResponse interface returning { id: string }
• Client-side validation of required fields before sending the request, with typeof/isNaN checks for numeric coordinates to correctly accept 0 as a valid value
• Follows the same pattern established by LineService.create

New files

• model/location/location-creation-request.ts — request interface
• model/location/location-created-response.ts — response interface

Modified files

• services/location/location.ts — create function implementation
• services/location/location.service.ts — service export with JSDoc
• services/location/location.service.spec.ts — 15 new tests
• public-api/model.ts — type exports

Test plan

• All 26 location service tests pass (15 new)
• TypeScript compiles with no errors (tsc --noEmit)
• Verify POST /locations works against a running backend with required fields only
• Verify optional fields (openingHours, inputFields, languages) are passed through correctly