POST /api/v1/partners/<pk>/impersonate/ mints a short-lived JWT for the
partner's primary partner_manager user. Returns access + refresh tokens
so the partner portal can create a session without requiring a password.
Writes a partner.impersonated audit log row with admin username, partner
name, and impersonated user for traceability.
Closes: admin Login-as-Partner showing "Partner not found" (mock data)
Sicherhaven
05de552820