feat(review 006 Unit 2): additive OperationSpec.description disclosed via discovery (E-02)

- OperationSpec gains description: Option<String> (builder
  with_description, defaults None; no struct-literal construction
  sites exist, so additive by construction)
- spec_to_json_pub emits description when set; rebuild_spec_for
  parses it back — the field survives from_call discovery and
  op/register announcement (same round-trip pattern as
  resource_id_path / publish_schema)
- services/list and the local-ops half of services/list-peers emit
  description when set; output-schema docs on both listing specs and
  operation_spec_schema advertise the field
- Tests: builder/default, emit/omit, listing emission, schema
  disclosure, schema-doc presence, round-trip + absent-stays-absent
  (8 new; 616 total)
- Docs: review 006 Unit 2 marked IMPLEMENTED; ADR-047 §6 amendment
  records the E-02 discovery decision (listing enrichment lands, the
  channel/resources/subscribe half stays deferred); OQ-40 gains the
  load-bearing note; operation-registry.md struct + listing docs;
  CHANGELOG

Verification: cargo test (616 pass), clippy -D warnings (host +
wasm32), fmt --check, cargo doc --no-deps, wasm32 check — all clean

docs/architecture/operation-registry.md

@@ -39,6 +39,9 @@ pub struct OperationSpec {
     pub output_schema: Value,     // JSON Schema for output
     pub error_schemas: Vec<ErrorDefinition>,  // Declared domain errors (ADR-016)
     pub access_control: AccessControl,
+    /// Human-readable op description (review 006 E-02). Disclosed by
+    /// `services/list` when set; `None` when the op declares none.
+    pub description: Option<String>,
     /// JSON pointer into the input for the resource ID, when
     /// `access_control.resource_type` is set and the operation targets a
     /// specific runtime-spawned resource (ADR-011). e.g., `"$.containerId"`
@@ -829,6 +832,12 @@ These are read-only — no admin operations are exposed through the call protoco
 }
 ```
 
+Each listing entry also carries `description` (review 006 E-02) when
+the op's spec declares one (`OperationSpec.description`, set via
+`with_description`) — the field is additive and absent otherwise. It
+describes the op, not the produced resource set: live resource
+discovery stays with `channel/resources/subscribe` (ADR-047 §6, OQ-40).
+
 `services/schema` accepts `{ "name": "fs/readFile" }` (no leading slash —
 registry form, same as `OperationSpec.name`) and returns the full
 `OperationSpec` including input/output JSON Schemas and declared