Replace the My Book Notes modal with ol-dialog

### Summary

On a book page, the **Notes** link in the sidebar opens the **My Book Notes** modal, which is built on the old jQuery colorbox. Rebuild it on ``, and use the rest of our web components inside it: `` for the actions, `showToast()` / `` for feedback, and an `` confirmation instead of the browser's `confirm()`.

Related: #13651 and #13652 (the same change for the Wikipedia citation dialog and the Share modal)

### How to find it

1. Log in and open any edition page, e.g. `http://localhost:8080/books/OL6M`.
2. In the sidebar links (next to Review and Share), click **Notes**. It appears on both desktop and mobile.
3. Saved notes also show up on your notes page in My Books (`/people//books/notes`), which is useful for checking that save and delete worked.

### Current implementation

- **Markup:** `openlibrary/macros/NotesModal.html`, rendered from `openlibrary/templates/type/edition/modal_links.html`
- **JS:** `initNotesModal` in `openlibrary/plugins/openlibrary/js/modals/index.js`, wired up in `js/main.js`
- Save and delete POST to `/works//notes.json` via `$.ajax`.
- Delete uses `confirm('Really delete this book note?')`.
- Feedback uses the legacy `FadingToast`, and colorbox closes the modal.
- The toast strings and the confirm string are hardcoded English and not translatable.
- **Buttons:** legacy `cta-btn cta-btn--delete` / `cta-btn--shell`

### Components to use

| Need | Component | Reference |
|---|---|---|
| Dialog | `` | `openlibrary/components/lit/OlDialog.js`; the ["Form dialog" example](https://openlibrary.org/developers/design/components#demo-dialog-form-trigger) under [Dialog on the Components design page](https://openlibrary.org/developers/design/components#dialog) is almost exactly this UI |
| Save / Delete / Cancel | `` | `OLButton.js`, the "Variants" example under [Button](https://openlibrary.org/developers/design/components#button) |
| Delete confirmation | a second small `` | the ["Confirmation" example](https://openlibrary.org/developers/design/components#demo-dialog-confirm-trigger) ("Delete this list?") under Dialog |
| Success/error feedback | `showToast()` | `openlibrary/components/lit/OlToastRegion.js`, the "Imperative use" example under [Toast](https://openlibrary.org/developers/design/components#toast) |

Read `docs/ai/design.md` and `docs/ai/web-components.md` before starting.

### Acceptance criteria

- [ ] Clicking **Notes** opens an `` titled "My Book Notes", on both desktop and mobile (consider `fullscreen-on-mobile`).
- [ ] The textarea is prefilled with the saved note, and focus lands in it when the dialog opens.
- [ ] **Save** uses ``, POSTs the note, closes the dialog and shows a success toast.
- [ ] **Delete** only appears when a note exists. It uses `` and asks for confirmation in an ``. On confirm it deletes the note, clears the textarea, hides Delete and shows a toast.
- [ ] Failed requests show an error toast and keep the dialog open, so the note isn't lost.
- [ ] Logged-out patrons still get the existing login redirect (`notes-modal-link--redirect js-login-intent`).
- [ ] `fetch` replaces `$.ajax`, with no new jQuery.
- [ ] Every user-facing string, including the toasts and the confirmation, is translatable (see `docs/ai/i18n.md`).
- [ ] The notes colorbox wiring and legacy markup are removed. Leave the Review (`ObservationsModal`) modal and the My Books notes page alone; they're out of scope.
- [ ] Keyboard works end to end: Tab stays inside the dialog, Escape closes it and focus returns to the Notes link.