v0.16.0

This release explicitly targets Hubuum server v0.0.20.

Security

• Update rustls-webpki to 0.103.16 and webpki-root-certs to 1.0.10 for
  RUSTSEC-2026-0382 and RUSTSEC-2026-0383.

Added

• Opt-in login_session(credentials, client_id) for the server's versioned
  interactive session API, with sync/async parity. Cloned clients serialize
  refresh and atomically replace both credentials. Passwords are not retained;
  refresh credentials remain in memory and are never automatically retried.
• session_info() exposes non-secret deadlines; session_providers() discovers
  providers on the versioned API. Legacy login and explicit PAT injection remain
  available for older servers and service credentials, respectively.

Changed

• Breaking server target: upgrade to Hubuum v0.0.20 and use
  login_session for interactive authentication. Older server login routes are
  unavailable on this server. Upgrade API, worker, and restore binaries together
  during the documented offline migration; keep a pre-upgrade backup for rollback.
• Recognize backup format 10 and the 257-operation OpenAPI contract. New history,
  hydration, credential activity, and observation-management operations are
  available through raw(); see the documented typed API gaps.
• Refresh all dependencies compatible with Rust 1.88 and all GitHub Actions pins,
  including the HTTPmock 0.9 test API.
• Breaking: Client token() and deprecated get_token() now return
  Result<Token, ApiError> snapshots instead of borrowed strings, and
  token_expires_at() returns an owned timestamp. Callers must handle unavailable
  session credentials and use client.token()?.as_str() when raw bearer access
  is necessary. A refresh failure, cancellation, or ambiguous response requires
  login again; logout clears session credentials across clones.
• Enable Tokio's sync feature for async refresh coordination. The Rust 1.88
  MSRV and supported public feature combinations remain unchanged.