feat(http): initialize alknet-http crate with module skeleton

Add crates/alknet-http with Cargo.toml, src/lib.rs, and the five
subsystem modules (server, gateway, client, adapters, websocket) per
ADR-039 (server + client host colocated). The mcp feature gate pulls in
rmcp with streamable HTTP transport features only (ADR-037 — no stdio);
h3/WebTransport is absent (deferred per ADR-044). alknet-core and
alknet-call use workspace path deps. The crate is added to the workspace
members list.

crates/alknet-http/src/lib.rs

@@ -0,0 +1,13 @@
+//! alknet-http: HTTP interface for alknet — serves HTTP/1.1 + HTTP/2 on
+//! standard ALPNs (with WebSocket upgrade for browser bidirectional access)
+//! and hosts the HTTP-backed call-protocol adapters.
+//!
+//! Two roles in one crate (ADR-039): HTTP server (HttpAdapter, a
+//! ProtocolHandler for h2/http1.1 + WS upgrade) and HTTP client host
+//! (from_openapi/from_mcp forwarding, to_openapi/to_mcp projections).
+
+pub mod adapters;
+pub mod client;
+pub mod gateway;
+pub mod server;
+pub mod websocket;