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/toggle.tsx

@@ -0,0 +1,46 @@
+"use client";
+
+import { Toggle as TogglePrimitive } from "@base-ui/react/toggle";
+import { cva, type VariantProps } from "class-variance-authority";
+import type React from "react";
+import { cn } from "@/lib/utils";
+
+export const toggleVariants = cva(
+  "relative inline-flex shrink-0 cursor-pointer select-none items-center justify-center gap-2 whitespace-nowrap rounded-lg border font-medium text-base text-foreground outline-none transition-shadow before:pointer-events-none before:absolute before:inset-0 before:rounded-[calc(var(--radius-lg)-1px)] pointer-coarse:after:absolute pointer-coarse:after:size-full pointer-coarse:after:min-h-11 pointer-coarse:after:min-w-11 hover:bg-accent focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-1 focus-visible:ring-offset-background disabled:pointer-events-none disabled:opacity-64 data-pressed:bg-input/64 data-pressed:text-accent-foreground sm:text-sm [&_svg:not([class*='opacity-'])]:opacity-80 [&_svg:not([class*='size-'])]:size-4.5 sm:[&_svg:not([class*='size-'])]:size-4 [&_svg]:pointer-events-none [&_svg]:-mx-0.5 [&_svg]:shrink-0",
+  {
+    defaultVariants: {
+      size: "default",
+      variant: "default",
+    },
+    variants: {
+      size: {
+        default: "h-9 min-w-9 px-[calc(--spacing(2)-1px)] sm:h-8 sm:min-w-8",
+        lg: "h-10 min-w-10 px-[calc(--spacing(2.5)-1px)] sm:h-9 sm:min-w-9",
+        sm: "h-8 min-w-8 px-[calc(--spacing(1.5)-1px)] sm:h-7 sm:min-w-7",
+      },
+      variant: {
+        default: "border-transparent",
+        outline:
+          "border-input bg-background not-dark:bg-clip-padding shadow-xs/5 not-disabled:not-active:not-data-pressed:before:shadow-[0_1px_--theme(--color-black/4%)] dark:bg-input/32 dark:data-pressed:bg-input dark:hover:bg-input/64 dark:not-disabled:not-active:not-data-pressed:before:shadow-[0_-1px_--theme(--color-white/6%)] dark:not-disabled:not-data-pressed:before:shadow-[0_-1px_--theme(--color-white/2%)] [:disabled,:active,[data-pressed]]:shadow-none",
+      },
+    },
+  },
+);
+
+export function Toggle({
+  className,
+  variant,
+  size,
+  ...props
+}: TogglePrimitive.Props &
+  VariantProps<typeof toggleVariants>): React.ReactElement {
+  return (
+    <TogglePrimitive
+      className={cn(toggleVariants({ className, size, variant }))}
+      data-slot="toggle"
+      {...props}
+    />
+  );
+}
+
+export { TogglePrimitive };