backend: per-doctor patient visibility, transfer, provider picker & scoped activity

- Add patients.primary_provider_id (FK to user) + migration; persist it through
  create/update and surface it on the Patient shape.
- Scope patient list/get for the `doctor` role to their own panel (with a
  createdBy fallback for legacy rows); admin/owner/member/reception/viewer keep
  seeing every patient.
- Add POST /api/patients/:fileNumber/transfer to reassign a chart (updates the
  provider link + PCP label, records activity, notifies the clinic).
- Add GET /api/staff/providers (any member) listing clinical-capable members for
  the PCP picker and transfer dialog.
- Scope the activity feed: non-admins see only their own actions; owners/admins
  see the whole clinic.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/types/patient.ts

@@ -57,7 +57,8 @@ export type Patient = {
   name: string;
   age: number;
   sex: Sex;
-  pcp: string; // primary care provider
+  pcp: string; // primary care provider (display name)
+  primaryProviderId?: string | null; // user id of the responsible clinician
   status: PatientStatus;
   initials: string; // for AvatarFallback
   allergies: Allergy[];