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/index.ts

@@ -8,6 +8,7 @@ import { errorHandler, notFound } from "./middleware/error.js";
 import { appointmentsRouter } from "./routes/appointments.js";
 import { notesRouter } from "./routes/notes.js";
 import { patientsRouter } from "./routes/patients.js";
+import { prescriptionsRouter } from "./routes/prescriptions.js";
 
 const app = express();
 
@@ -47,6 +48,7 @@ app.get("/health", (_req, res) => {
 app.use("/api/patients", patientsRouter);
 app.use("/api/notes", notesRouter);
 app.use("/api/appointments", appointmentsRouter);
+app.use("/api/prescriptions", prescriptionsRouter);
 
 app.use(notFound);
 app.use(errorHandler);
@@ -57,4 +59,5 @@ app.listen(env.PORT, () => {
   console.log(`  • patients: /api/patients`);
   console.log(`  • notes:    /api/notes`);
   console.log(`  • appts:    /api/appointments`);
+  console.log(`  • rx:       /api/prescriptions`);
 });