Add focused test coverage for the useNotes React hook

[diogobaltazar]

Summary

Add focused test coverage for the useNotes React hook.

This repo already has one hook test file for useActivityGraph, but useNotes has meaningful state transitions and no tests. That makes it a good 1-2 hour exercise: contained logic, clear inputs, and obvious validation.

Current State

Relevant files:

• src/move37/sdk/node/src/hooks/useNotes.js
• src/move37/sdk/node/src/hooks/useActivityGraph.test.jsx

useNotes currently handles:

• initial note loading
• createNote(...)
• updateNote(...)
• importTxtNotes(...)
• error state management

None of that is currently covered by tests.

Acceptance Criteria

• Add a test showing the hook loads notes on mount.
• Add a test showing createNote(...) inserts or prepends the returned note into local state.
• Add a test showing updateNote(...) replaces the existing note entry rather than duplicating it.
• Add a test showing importTxtNotes(...) adds imported notes to local state.
• Add at least one error-path test showing the hook exposes an Error instance when the request fails.
• Follow the existing test style used in useActivityGraph.test.jsx.

Non-Goals

• Do not refactor the hook implementation unless needed to make the tests pass.
• Do not add a new hook abstraction layer.
• Do not modify the backend for this issue.

Validation

Run:

cd src/move37/sdk/node
npm test

Please keep the tests readable. This issue is meant to reveal whether the candidate can use an agent for speed without outsourcing basic judgment about state transitions.