Two simplify-pass cleanups:
- vault-status.ts: VaultStatus is now an alias of GetVaultStatusResponse['data']
instead of a re-declared 4-field interface, so the renderer's input shape is
single-sourced from the message contract and can't drift from the SW handler.
- service-worker/vault.ts: handleGetVaultStatus counts active items via the
existing listItems() helper rather than re-implementing the trashed_at filter.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>