The offline, cancelled, and generic-fallback branches hardcode `redirects: nil`

> Split out from Automattic/wordpress-rs#1497 — *Swift executor URLSession error audit*. Section E — Cancellation gaps.
>
> File references are to `native/swift/Sources/wordpress-api/SafeRequestExecutor.swift` unless noted; `:NNN` line numbers were verified against `fix/converge-executor-error-classification`.

**Severity: low.** `handleHttpsError` and `handleNonExistentSiteError` attach `executorDelegate.redirects(for:)`; the other three failure branches don't, losing the redirect trail for a request that redirected and then died mid-transfer, was cancelled, or failed unclassified. `redirects(for:)` returns `nil` when no redirects occurred, so attaching it everywhere is behavior-neutral in the common case. Overlaps the payload half of Automattic/wordpress-rs#1503; looks like an oversight rather than a decision.

Start in native/swift/Sources/wordpress-api/SafeRequestExecutor.swift, reading handleHttpsError and handleNonExistentSiteError before locating the three failure branches in handleHttpsError that hardcode redirects: nil. Done means each failure path preserves executorDelegate.redirects(for:) while requests with no redirects remain unaffected.

Written by the indexing model from the issue text.