[PianoNic]

Summary

• The backend now sends a stable label key (the tool name, or generic for tools without a label) and structured args (page, unread only, folder, search, term count, sources, tool title) next to the existing English label and detail, in streaming events, stored transcripts and the conversation DTOs.
• The web app translates step labels, notes, the run summary, the repeat suffix, status words and screen-reader text from public/i18n/*.json in de, en, fr, it and rm, including the new search, list_subjects and list_assessments tools.
• The English label and detail stay as the fallback for unknown keys (plugin tools) and for stored conversations without a key, so old transcripts render as before.

Closes #615