Render NIP-98 url/method in the bunker approval screen

[kwsantiago]

PR privkeyio/keep#677 exposes http_auth (url, method) on BunkerApprovalRequest over the UniFFI boundary, populated for kind-27235 (NIP-98 HTTP auth) sign requests.

The approval screen (Nip46ApprovalScreen) should render the url and method so the user can see what a kind-27235 HTTP-auth signature authorizes instead of approving a blind bearer credential. A missing field should read as "unspecified" rather than be hidden (a malformed request the user should see).

Depends on the keep-mobile UniFFI bindings from privkeyio/keep#677 being published.

[kwsantiago]

Fixed in #417: the bunker approval screen (Nip46ApprovalScreen) now renders the NIP-98 HTTP url/method from BunkerApprovalRequest.httpAuth, gated on presence so a malformed kind-27235 (no u tag) shows 'Unspecified' rather than hiding the request (matching the signer-core contract and the keep-desktop surface). Untrusted rows are sanitized + line-capped; covered by HttpAuthRowsTest.