Add sync between main and sub windows when viewing notes

[ComputelessComputer]

Code: https://github.com/fastrepl/hyprnote/blob/e3e0c4b381a178858a60d27302cc4a743e6949ee/apps/desktop/src/components/editor-area/index.tsx#L192-L210

Context: Currently, we enforce a read-only state for notes opened in sub-windows (i.e., not the main view) to prevent conflicts, since editor sync between windows isn’t implemented yet.

Impact: Users cannot edit notes in sub-windows, even if they have permission, which limits multi-window workflows.

Next step: Once editor syncing is implemented, we can safely remove this restriction and allow full editing capabilities in all windows.