Add Calendar dialog, Prescriptions & Messages pages, note delete confirm

- Appointments: a Calendar button next to Add opens a month-grid dialog
  (reuses the Calendar primitive + shared ScheduleList); the schedule day is
  marked and selecting it lists that day's appointments.
- Patients sub-nav: new Prescriptions page (mock list + KPIs) with a compact
  "New prescription" dialog reusing the patient quick-search pattern.
- Notes: deleting a note now goes through a reusable ConfirmDialog instead of
  deleting immediately.
- New top-level Messages page: two-pane email-style inbox (list + reading pane
  with mock reply composer), mirroring the Notes layout.
- Sidebar logo bumped from size-9 to size-10.

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

frontend/components/ui/confirm-dialog.tsx

@@ -0,0 +1,63 @@
+"use client";
+
+import type { ReactNode } from "react";
+
+import { Button } from "@/components/ui/button";
+import {
+  Dialog,
+  DialogClose,
+  DialogDescription,
+  DialogFooter,
+  DialogHeader,
+  DialogPopup,
+  DialogTitle,
+} from "@/components/ui/dialog";
+
+// A small controlled confirmation dialog built on Dialog (there is no AlertDialog
+// primitive). Use for destructive actions: the confirm button is `destructive`
+// by default. onConfirm fires, then the dialog closes.
+export function ConfirmDialog({
+  open,
+  onOpenChange,
+  onConfirm,
+  title,
+  description,
+  confirmLabel = "Delete",
+  cancelLabel = "Cancel",
+  variant = "destructive",
+}: {
+  open: boolean;
+  onOpenChange: (open: boolean) => void;
+  onConfirm: () => void;
+  title: string;
+  description?: ReactNode;
+  confirmLabel?: string;
+  cancelLabel?: string;
+  variant?: "destructive" | "default";
+}) {
+  return (
+    <Dialog onOpenChange={onOpenChange} open={open}>
+      <DialogPopup className="sm:max-w-sm">
+        <DialogHeader>
+          <DialogTitle>{title}</DialogTitle>
+          {description && <DialogDescription>{description}</DialogDescription>}
+        </DialogHeader>
+        <DialogFooter variant="bare">
+          <DialogClose render={<Button type="button" variant="outline" />}>
+            {cancelLabel}
+          </DialogClose>
+          <Button
+            onClick={() => {
+              onConfirm();
+              onOpenChange(false);
+            }}
+            type="button"
+            variant={variant}
+          >
+            {confirmLabel}
+          </Button>
+        </DialogFooter>
+      </DialogPopup>
+    </Dialog>
+  );
+}