Migrate the partner-mode customer switcher, in-customer banner, sidebar tile and the team invite/teammate panels off the data/customers fixture onto the real /api/partner/tenants list (shared key, gated to partner-staff so the global shell doesn't 403 for other users). Active customer resolves by tenant _id (the key the customers page already passes to partnerMode.enter); partner-identity labels now use the real partner name from useMe. Removes the now-unused customers + CustomerOrg-list fixture export and the dead setCustomer helper. Verified in UI: switcher + enter/exit show real Baslund Test / Baslund Research ApS.
Move partner domain types out of data/customers.ts into types/partner.ts so the fixture data exports can be removed later without breaking type imports. Add usePartnerTenants / usePartnerMrr composables wrapping the shared-key partner fetches.