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/components/ui/toolbar.tsx

@@ -0,0 +1,91 @@
+"use client";
+
+import { Toolbar as ToolbarPrimitive } from "@base-ui/react/toolbar";
+import type React from "react";
+import { cn } from "@/lib/utils";
+
+export function Toolbar({
+  className,
+  ...props
+}: ToolbarPrimitive.Root.Props): React.ReactElement {
+  return (
+    <ToolbarPrimitive.Root
+      className={cn(
+        "relative flex gap-2 rounded-xl border bg-card not-dark:bg-clip-padding p-1 text-card-foreground",
+        className,
+      )}
+      data-slot="toolbar"
+      {...props}
+    />
+  );
+}
+
+export function ToolbarButton({
+  className,
+  ...props
+}: ToolbarPrimitive.Button.Props): React.ReactElement {
+  return (
+    <ToolbarPrimitive.Button
+      className={cn(className)}
+      data-slot="toolbar-button"
+      {...props}
+    />
+  );
+}
+
+export function ToolbarLink({
+  className,
+  ...props
+}: ToolbarPrimitive.Link.Props): React.ReactElement {
+  return (
+    <ToolbarPrimitive.Link
+      className={cn(className)}
+      data-slot="toolbar-link"
+      {...props}
+    />
+  );
+}
+
+export function ToolbarInput({
+  className,
+  ...props
+}: ToolbarPrimitive.Input.Props): React.ReactElement {
+  return (
+    <ToolbarPrimitive.Input
+      className={cn(className)}
+      data-slot="toolbar-input"
+      {...props}
+    />
+  );
+}
+
+export function ToolbarGroup({
+  className,
+  ...props
+}: ToolbarPrimitive.Group.Props): React.ReactElement {
+  return (
+    <ToolbarPrimitive.Group
+      className={cn("flex items-center gap-1", className)}
+      data-slot="toolbar-group"
+      {...props}
+    />
+  );
+}
+
+export function ToolbarSeparator({
+  className,
+  ...props
+}: ToolbarPrimitive.Separator.Props): React.ReactElement {
+  return (
+    <ToolbarPrimitive.Separator
+      className={cn(
+        "shrink-0 bg-border data-[orientation=horizontal]:my-0.5 data-[orientation=vertical]:my-1.5 data-[orientation=horizontal]:h-px data-[orientation=horizontal]:w-full data-[orientation=vertical]:w-px data-[orientation=vertical]:not-[[class^='h-']]:not-[[class*='_h-']]:self-stretch",
+        className,
+      )}
+      data-slot="toolbar-separator"
+      {...props}
+    />
+  );
+}
+
+export { ToolbarPrimitive };