fix(note): save the title from the shortcut and rename through the store

[mrsibe]

Closes #25.

Problem

Renaming a note could appear to do nothing until the list happened to reload:

• The Ctrl/Cmd+S "Save Note" shortcut only fired while the Tiptap body was
  focused (editor.isFocused in NoteEditor). Changing the title in the
  header field and pressing the shortcut silently did nothing — the field kept
  the typed value, so it looked saved, but nothing was written.
• The context-menu "Rename" action called window.api.updateNote directly and
  only relied on the optional onRefresh prop to re-fetch. The item store was
  left stale until the next loadItems — which is exactly the "create a new
  note and it finally updates" symptom.

Fix

• Move the shortcut:save-note listener from NoteEditor to
  NoteEditorPanel, which owns both the title input and the body, and save
  whenever focus is inside the panel. Remove the now-unused onSave prop.
• Route note renames through useItemStore.updateNote so the list and the
  editor read the same store; onRefresh still runs and still covers
  mind-map / quiz / anki renames.

Verification

Ran the built app (Electron) against a throwaway --user-data-dir with a
seeded notebook, driven over the DevTools protocol:

• focus the title input, change it, fire shortcut:save-note → the new title
  is written to notes and shown in the list (previously nothing happened)
• save from the focused editor body still works
• context-menu rename → list updates immediately and the DB matches

Static checks: npm run typecheck (node/web/test), npm run lint,
npm run check:design, npm test (22 pass), npx electron-vite build.

Not verified: manual clicking on a physical desktop session (interaction was
simulated via CDP against the real renderer).