Resolve a created link via GET /sdk/resolve. Returns the resolved link
body for live parity verification, or null if unreachable. This is the
lenient form the importer uses: any failure degrades to null so a live
import still completes.
Serialize our rich internal ULink link definition (see fdl_mapper.dart)
into the real POST /sdk/links request body. Anything the ULink schema has
no first-class field for (the in-app deep link, custom scheme, app ids, min
versions, and all attribution params) rides along in parameters with
allowQueryPassthrough so it is forwarded to the app on open — preserving
routing intent and attribution end to end.