feat(http): implement from_openapi adapter (OpenAPI parse + reqwest forwarding handlers)

Parses OpenAPI 3.x documents into HandlerRegistration bundles with
reqwest-backed forwarding handlers that inject credentials from
OperationContext.capabilities (no-env-vars invariant, ADR-014).
Error codes are prefixed HTTP_<status> (ADR-023); ops are Internal
leaves with FromOpenAPI provenance (ADR-015/022). SSE subscriptions
are consumed via parseSSEFrames; JSON/text/binary response branching
mirrors the TS prior art.

crates/alknet-http/src/adapters/mod.rs

@@ -8,4 +8,6 @@
 //! `docs/architecture/crates/http/http-adapters.md` and
 //! `docs/architecture/crates/http/http-mcp.md`.
 
-// TODO: implement
+pub mod from_openapi;
+
+pub use from_openapi::{FromOpenAPI, HttpAuthScheme, HttpServiceConfig, OpenAPISpec};