fix(note): stop destroying the Tiptap editor manually

[mrsibe]

What does this PR do?

Fixes the blank window that appears when clicking Add to Note in a chat while running the app in development.

Why?

NoteEditor registered a cleanup effect that called editor.destroy() on unmount, but @tiptap/react v3's useEditor already owns the editor lifecycle. Under React StrictMode (dev), effects run mount → cleanup → mount, so the second mount received an already destroyed instance; the content-sync effect then read editor.storage.markdown.getMarkdown() and threw. The renderer has no error boundary, so React unmounted the entire tree and the window went blank.

Production builds do not double-invoke effects, which is why the packaged app did not reproduce this.

This surfaced on Add to Note because #15 made that path open the note editor, mounting NoteEditor for the first time.

Related issue

No open issue; reported from manual testing.

What changed?

• Removed the manual editor.destroy() cleanup effect from NoteEditor and let useEditor manage teardown.
• Added a comment explaining why manual teardown must not be reintroduced.

How was this tested?

Reproduced and verified with Electron CDP against npm run dev (StrictMode active):

• Before: clicking "Add to Note" produced TypeError: Cannot read properties of undefined (reading 'getMarkdown') inside <NoteEditor>, and document.body.innerText.length dropped to 0 (blank window).
• After: the note editor mounts, the created note renders, opening/returning from notes and adding another note produce no exceptions.
• npm run typecheck:web passes.
• npm test passes (49/49).
• npx prettier --check src/renderer/src/components/notebook/note/NoteEditor.tsx passes.

Screenshots / recordings

Not applicable (no visual change when working).

Checklist

• I have reviewed my own changes.
• npm run typecheck passes.
• npm run build passes.
• I have tested the affected user workflow.
• I have not included unrelated changes.
• I have updated documentation when necessary.

Desktop / build changes

• Not applicable