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/server/mod.rs

@@ -0,0 +1,9 @@
+//! HTTP server: `HttpAdapter`, axum-over-QUIC, gateway routes, `/healthz`,
+//! decoy, and custom routes.
+//!
+//! Implements `alknet_core::types::ProtocolHandler` for the standard HTTP
+//! ALPNs (`h2`, `http/1.1`) with WebSocket upgrade for browser
+//! bidirectional access (ADR-044). See
+//! `docs/architecture/crates/http/http-server.md`.
+
+// TODO: implement