feat: org-scoped prescriptions backend, wire prescriptions page

Add the prescriptions table, validation, service and CRUD routes
(/api/prescriptions, RBAC-gated; prescriber defaults to the signed-in
clinician, prescribedAt to today) and the frontend data module. The page
now loads/persists real data and computes its status KPIs.

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

backend/src/types/prescription.ts

@@ -0,0 +1,21 @@
+// The canonical Prescription shape returned by the API. Mirrors the frontend
+// `lib/prescriptions.ts` Prescription type. Scoped to the active clinic; patient
+// fields are denormalized for display and `fileNumber` links to a patient.
+export type PrescriptionStatus = "active" | "completed" | "expired";
+
+export type Prescription = {
+  id: string;
+  fileNumber: string;
+  name: string;
+  initials: string;
+  medication: string;
+  dose: string;
+  frequency: string;
+  prescriber: string;
+  prescribedAt: string; // YYYY-MM-DD
+  status: PrescriptionStatus;
+  duration: string | null;
+  notes: string | null;
+  createdAt: string;
+  updatedAt: string;
+};