Add Notes page: Tiptap rich-text editor backed by the notes API

- lib/notes.ts: list/get/create/update/delete via the API client.
- New /notes route + nav item (and shared lib/nav.ts entry, i18n key) so it
  shows in the sidebar and command palette.
- components/notes/notes-view.tsx: a note list + "New note", with save/delete
  and toasts.
- components/notes/notes-editor.tsx: a Word-like COSS Toolbar driving Tiptap
  (StarterKit + Placeholder) — bold/italic/underline, H1–H2, bullet/numbered
  lists, undo/redo — plus a title field and Save. Installed @coss/toolbar and
  @coss/toggle-group and the Tiptap packages.

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

frontend/lib/notes.ts

@@ -0,0 +1,39 @@
+import { apiFetch } from "@/lib/api-client";
+
+// A doctor's note. `content` is rich-text editor HTML. Mirrors the backend
+// `src/types/note.ts`. Notes are scoped to the active clinic + signed-in author.
+export type Note = {
+  id: string;
+  title: string;
+  content: string;
+  createdAt: string;
+  updatedAt: string;
+};
+
+export type NoteInput = { title: string; content: string };
+
+export function listNotes(): Promise<Note[]> {
+  return apiFetch<Note[]>("/api/notes");
+}
+
+export function getNote(id: string): Promise<Note> {
+  return apiFetch<Note>(`/api/notes/${id}`);
+}
+
+export function createNote(input: NoteInput): Promise<Note> {
+  return apiFetch<Note>("/api/notes", {
+    method: "POST",
+    body: JSON.stringify(input),
+  });
+}
+
+export function updateNote(id: string, input: NoteInput): Promise<Note> {
+  return apiFetch<Note>(`/api/notes/${id}`, {
+    method: "PUT",
+    body: JSON.stringify(input),
+  });
+}
+
+export function deleteNote(id: string): Promise<void> {
+  return apiFetch<void>(`/api/notes/${id}`, { method: "DELETE" });
+}