Add GET /api/v1/specialties/doctor-counts?city_id= returning every active
specialty with number_of_doctors (distinct doctors via doctor_specialties,
scoped by doctor_cities when city_id is given). Make /api/v1/specialties GET
public. Powers the /specialties page count. Docs updated.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
