Adds a CREDS/REUSE tab segment on the Credential Vault page. The REUSE
tab lists CredentialReuse rows (paginated 25 per page) ordered by
target_count desc; row-click opens a drawer mirroring the credentials
inspector with a deckies x services grid, attacker links, and a
PROFILING PENDING placeholder when attacker_uuids has not been
backfilled yet.
The CREDS tab gains a REUSE column showing a clickable target-count
badge for credentials whose (sha256, kind, principal) tuple matches a
reuse row; clicking the badge fetches and opens that row's drawer.
Section header gains a manual refresh button (no SSE/polling).
Ticks the credential-reuse line in DEVELOPMENT.md and notes the
vectorstore scaffold.