fix(gateway): publish validation + streaming + batch semantics (GW-01, GW-06, GW-08..GW-11, HY-13)

- GW-01: /publish validates every NDJSON chunk against the op's
  publish_schema (incl. the first-line chunk) via NdjsonChunkStream —
  terminal Err(INVALID_INPUT)/422 on violation, matching the wire
  dispatcher's per-chunk contract. Route-level fix; the alkcall spine
  was explored and rejected (wire validation is pump-side by design).
- GW-06: the body is streamed, not buffered — Body::into_data_stream()
  -> newline-framed BufferedLines -> lazily parsed chunk stream.
  ADR-068 documents the streamed semantics and the 2 MiB per-line cap.
- GW-08: /batch capped at 100 operations (INVALID_INPUT 400).
- GW-09: internal-op batch entries now carry generated UUID request ids.
- GW-10: first publish line missing `chunk` is rejected INVALID_INPUT.
- GW-11: redundant /publish pre-checks removed; enforcement rides on
  invoke_sink via the shared dispatch spine.
- HY-13: the vacuous stub test was replaced by a body-cut-short test.
- Adjacent: INVALID_OPERATION_TYPE now maps 422 (with identity) / 401
  (without) in error.rs — the route relies on the shared mapper since
  the pre-checks are gone (GW-03's finding; was a 500 fall-through).

Verification: cargo test 211 passed; cargo clippy --all-targets -- -D
warnings clean; cargo fmt --check clean.

Cargo.toml

@@ -45,6 +45,7 @@ openapiv3 = "2"
 http = "1"
 url = "2"
 bytes = "1"
+jsonschema = { version = "0.46", default-features = false }
 parking_lot = "0.12"
 rmcp = { version = "1.8", optional = true, default-features = false, features = [
     "client",