Internal code-comment cleanup in batch Mail Contents view (no functional change)

This change updates a single source-code comment in the batch Mail Contents component for readability. There is no change to application behavior, data, or the user interface.

During ongoing maintenance of the batch Mail Contents view, a developer comment describing a piece of internal logic was reworded for clarity. Keeping in-code documentation accurate helps engineers maintain the area more confidently and reduces the chance of future misunderstandings.

No user-facing or client-facing impact. End users will see no difference in the application. The benefit is internal: slightly clearer code for the engineering team working on the Mail Contents area.

• Edited one comment line in src/components/batches/TabContents/MailContents/MailContents.tsx (1 line changed: +1 / -1).
• The comment above a React useEffect (which syncs the selected status when the URL state changes) was reworded.
• No logic, imports, props, or rendered output were modified.

Effectively zero risk. The change touches only a comment and does not alter compiled output or runtime behavior. No mitigation required beyond a standard build/lint pass.

No dedicated QA is required. As a sanity check, confirm the frontend builds and lints cleanly and that the batch Mail Contents view continues to load and update the selected status correctly when navigating via URL state.