PROD-1506: create/update URL redirections on sync/push with ID mappings

[jules-exel]

Summary

URL redirections were downloaded on pull (via the Content Sync SDK) but never pushed to the target. This adds a full create/update push path with source→target ID mappings, using the new Management API batch endpoint:

POST /api/v1/instance/{guid}/url-redirections — accepts up to 250 redirections per request (one transaction per request). Items without a urlRedirectionID are created; items with one are updated (full replace). Per-item results come back grouped into created / updated / skipped.

How it works

• New UrlRedirections element, included in the default --elements list and registered as a guid-level push operation. It runs after Containers and before Templates — the template pusher deliberately throws on mapping inconsistencies (rename protection), which aborts the rest of the guid-level loop, and dependency-free redirections must not be collateral damage of that stop.
• Change detection is a direct field diff of pulled source vs target items (redirections carry no modifiedOn): mapped + identical → skip; mapped + different → update; same origin URL without a mapping → map-on-adopt (self-heal, consistent with galleries/models); otherwise → create. A mapped redirect deleted on the target is re-created. Deletes do not propagate (consistent with all other pushers).
• Batching: creates and updates are sent together in chunks of 250 sequential requests. The response's per-item index (position within that request's payload) is used to write sourceUrlRedirectionID → targetUrlRedirectionID rows to a new central mapping file at agility-files/mappings/{source}-{target}/urlredirections/mappings.json. API-side skips (validation failures / origin URL collisions) are logged with their reason. A failed batch marks only its own items failed and the run continues with the next batch; re-runs self-heal via the diff + map-on-adopt.
• Field mapping: pulled sync data uses id/statusCode; the payload sends urlRedirectionID/httpCode.
• Preflight: full --preflight support under a "URL Redirections" phase; mapping writes remain behind the existing preflight hard guard.
• The endpoint isn't in @agility/management-sdk yet, so url-redirection-api.ts calls it directly with the same token/base-URL resolution the SDK client uses.

Behavior notes

• A plain agility sync now pushes redirections by default (they were already always downloaded). Scope with --elements to exclude them.
• Target-only redirections are never touched; a source redirect deleted after a previous sync stays on the target (delete propagation would need an API delete endpoint — future work).