test+docs: prepublish hardening from review (failure paths, doc hygiene)

Coverage:
- CF-002: demux skipped-bytes budget teardown test (268 MiB skip in-memory;
  a budgetless demux wedges in the 17th skip, the real one tears down) and
  the skip-hits-EOF arm (truncated oversized payload ends the loop).
- CF-001: retryable CONNECTION_CLOSED pinned for subscribe write failures
  in both stream modes and single-stream publish request-frame failures;
  non-retryable INTERNAL pinned for mid-publish failures in both modes
  (deterministic FailOnFlushN write half).
- Gateway: invoke_sink with with_deadline(None) completes a slow sink.

Docs:
- Fix broken intra-doc link on lib.rs's feature-gated gateway mention
  (rustdoc warned on default-feature builds).
- Re-point 40 src/ references from the old alknet mono-repo ADR numbering
  (049/050/052/065/070/074/092) to this crate's numbering
  (021/011/034/007/008/009/005); drop into_sub_streams references
  removed by ADR-035.

Verification: 565 default / 582 all-features (8 new), clippy -D warnings
on default/gateway/all-features/wasm32, fmt clean, rustdoc warning-free
on default and all-features, publish dry-run clean. Consumer-facing API
continuity 0.1.1 -> 0.2.0 verified by compiling an API-surface probe
against both versions.

src/channels/wire.rs

@@ -23,7 +23,7 @@ use thiserror::Error;
 pub const CHUNK_HEADER_LEN: usize = 8;
 
 /// The maximum chunk payload length (16 MiB, matching TTY's cap —
-/// ADR-052 §5). A chunk with `length > MAX_CHUNK_LEN` returns
+/// ADR-034). A chunk with `length > MAX_CHUNK_LEN` returns
 /// [`ChunkError::TooLarge`] and does not corrupt the stream — the demux
 /// drops the chunk and continues. The header is always exactly 8 bytes,
 /// so the demux can always resync by reading the next 8-byte header.