deps: the alkcall substrate pin + the batch-1 module skeleton

- Cargo.toml: alkcall = "0.8.0" (convention 11 — pinned, first
  consumption of the 0.8.0 surface), serde/serde_json, bytes, and
  the std-only futures subset (BoxFuture seam shape). tokio's
  wasm-clean subset and the empty local/composed features unchanged.
- lib.rs: the six skeleton modules per overview.md §Module Map
  (params, wire, producer, consumer, egress, error) — stub files
  with module docs naming their filling tasks; no re-exports yet
  (each implementation task adds its own).

Verified: cargo test (76 tests), clippy --all-targets -D warnings,
fmt --check, cargo doc --no-deps, both wasm checks
(check + clippy on wasm32-unknown-unknown), and the dep-graph
spot-checks (no mio/socket2/tokio::net in the default normal graph;
normal tokio features = bytes/io-util/macros/rt/sync/time only).
alkcall 0.8.0 from crates.io confirmed wasm-clean via probe build
before wiring.

Task: tasks/implementation/core-crate-deps.md (completed)

src/error.rs

@@ -0,0 +1,3 @@
+//! `SocksError` + the typed open-error surface (alkcall ADR-049 §4).
+//!
+//! Stub: filled by the `implementation/core-params-errors` task.