Add logout, passkey management, and a standalone login

The "auth routes" open question in GOALS.md conflated four unrelated
things once the upstream routes and controllers were checked: logout and
the passkey settings routes sit behind the same token_auth middleware as
everything else this crate wraps, login needs a credential exchange since
there's no token yet, refresh/refresh_react turned out to be the bulk
sync-dump endpoint already parked as a separate open question, and
connected_account is Gmail OAuth linking that belongs with Integrations.

Adds logout, list_passkeys, delete_passkey (passkey registration is left
out — it needs a WebAuthn ceremony a browser has to drive), and
InvoiceNinjaClient::login as an associated function returning a lean
LoginResponse that types only is_owner/is_admin/token and leaves the
server's much larger nested payload in extra.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/decode_tolerance.rs

@@ -72,6 +72,9 @@ fn every_model_absorbs_a_null_or_missing_field() {
         Invoice,
         InvoiceItem,
         Location,
+        LoginCompanyUser,
+        LoginResponse,
+        Passkey,
         Payment,
         PaymentInvoice,
         PaymentTerm,