fix: ensure editor receives focus after creating a new note

[j4rviscmd]

Summary

• Blur the "+" button before invoking onNewNote so it no longer holds browser focus after a new note is created
• Change focusEditor in useCursorMemory to use a double requestAnimationFrame, ensuring the ProseMirror view has fully settled before focusing the editor

Test plan

• Click the "+" button to create a new note and verify the editor receives focus
• Switch between existing notes from the sidebar and verify focus still works
• Restart the app and verify cursor position restoration and focus work correctly
• Hide/show the window and verify focus behavior is unchanged

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