fix: clear stale Notes tab error message

[Atreus-X]

Summary

• The Notes tab's create-note error (for example a name that already exists) stayed on screen until the next successful create, even after the note was deleted or another note was selected.
• It now clears when you select a note, delete one, click New note, type in the name box, or press Escape.

Notes

• UI only; no host or transport involved, so SSH and wsh behave the same.
• Branched from main, no stacking.
• Library-wide errors (snippet save, list refresh) are a separate banner and are unchanged.

Test plan

• npx tsc --noEmit: no errors in library.tsx
• npx vitest run: passes
• Create a note with a name that already exists: error shows; delete or select another note: error clears
• Error also clears when you type in the name box or press Escape

🤖 Generated with Claude Code

https://claude.ai/code/session_01W6QMXXvRReaKxWk1JL5Et6