feat(http): move from_jsonschema to alknet-http as real HTTP-backed adapter (ADR-066)
- Add FromJsonSchema adapter in alknet-http with reqwest forwarding handler
reusing from_openapi's build_request/forward/forward_stream logic
- Delete broken placeholder from alknet-call (NOT_FOUND-returning handler)
- Keep FromJsonSchema variant in OperationProvenance (alknet-call)
- Make forwarding functions pub(crate) in from_openapi.rs for reuse
- 11 tests: unit (provenance, handler kind, path/query, bearer injection,
no-env-vars) + integration (echo server, non-2xx errors, SSE streaming)