#925 feat(notebooks): add list view toggle to notebooks page

Summary

Adds a tile/list view toggle to the Notebooks page, addressing the navigation pain of large notebook collections.

• Tile view (default, unchanged): the existing visual card grid.
• List view: compact rows showing notebook name, description, source/note counts, and last updated — easier to scan when you have many notebooks.
• A segmented toggle (grid/list icons) in the page header switches between modes.
• The preference is persisted via a Zustand store (notebook-view-storage) so it survives reloads and is shared by both the active and archived lists.

Frontend-only — no API changes. NotebookResponse already exposes source_count, note_count, updated, name, and description.

Changes

• New notebook-view-store.ts (persisted Zustand store).
• New NotebookRow.tsx — compact row variant reusing the card's click-to-open / archive / delete behavior.
• NotebookList.tsx renders the grid or the row list based on the store.
• Toggle control added to notebooks/page.tsx header.
• New notebooks.tileView / notebooks.listView keys translated across all 14 locales.
• CHANGELOG updated under [Unreleased].

Verification

• tsc --noEmit clean, npm run lint 0 errors, locale parity test 14/14.
• Verified locally with Playwright: toggling switches layouts, the active button highlights, and the list-view selection persists across a full page reload.

Closes #885