Redesign Calendar + Messages, fix favicon, add date picker, Tasks & Activity

- Appointments now carry a date; the Calendar button opens a Google-Calendar
  style month grid (color-coded event chips, month nav, Today, click a day for
  its list). Today/Upcoming sections derive from dates.
- Add-appointment dialog gains a date picker (Popover + Calendar).
- Messages rebuilt as chat threads: an input-based composer that appends to a
  two-way timeline (no more toast covering the field), and the unread count is
  now a filter toggle.
- Favicon: the brand logo now shows in the tab. Removed the stale default
  app/favicon.ico (which shadowed it) and added app/icon.png + app/apple-icon.png
  generated from the logo; dropped the redundant metadata.icons.
- Sidebar: swapped Notes <-> Messages order (both kept).
- New pages: Activity (signed-change audit timeline with hash chips + approval
  status) and Tasks (two-pane care-team to-do with add dialog).
- Prescriptions: adding a medication now surfaces mock drug-interaction and
  allergy warnings against the patient's record.

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

frontend/app/(app)/activity/page.tsx

@@ -0,0 +1,10 @@
+import { ActivityView } from "@/components/activity/activity-view";
+import { SidebarInset } from "@/components/ui/sidebar";
+
+export default function ActivityPage() {
+  return (
+    <SidebarInset className="flex flex-1 flex-col overflow-y-auto">
+      <ActivityView />
+    </SidebarInset>
+  );
+}