feat(adapters): from_jsonschema single-endpoint adapter + shared forwarding core

- src/adapters/forward.rs: shared HTTP forwarding core (extracted from
  old from_openapi) — HttpServiceConfig/HttpAuthScheme, build_request
  with capabilities-based credential injection (no env vars), forward
  + forward_stream (SSE projection), parse_sse_frames
- src/adapters/from_jsonschema.rs: FromJsonSchema OperationAdapter
  (ADR-066) — one registration per call, FromJsonSchema provenance
  (leaf, Internal default), Sub -> HandlerKind::Stream (text/event-stream)
- adapted to alkcall 0.1.1: OperationType::Sub, alkcall::client
  adapter traits

Verified: cargo test (106 lib tests), clippy -D warnings, fmt.

src/adapters/mod.rs

@@ -1 +1,10 @@
+//! HTTP-backed call-protocol adapters: `from_openapi` / `from_jsonschema`
+//! (import external HTTP APIs as operations), `to_openapi` / `to_mcp`
+//! (project local operations onto HTTP surfaces), `from_mcp`, and
+//! `from_wss` (feature `wss`).
 
+pub mod forward;
+pub mod from_jsonschema;
+
+pub use forward::{HttpAuthScheme, HttpServiceConfig};
+pub use from_jsonschema::FromJsonSchema;