feat(call): introduce StreamingHandler, HandlerKind, ResponseStream + INVALID_OPERATION_TYPE (ADR-049)

Add the foundational types for ADR-049 streaming handlers:
- StreamingHandler, ResponseStream type aliases and HandlerKind enum
  (Once | Stream) in registration.rs, with make_streaming_handler() helper
- CallError::invalid_operation_type() in wire.rs (sixth protocol code,
  retryable: false)
- HandlerRegistration.handler flipped from Handler to HandlerKind;
  HandlerRegistration::new() now takes HandlerKind
- OperationRegistryBuilder absorbs wrapping: with_local/with_leaf/
  with_leaf_provenance wrap raw Handler in HandlerKind::Once for
  Query/Mutation; new with_local_streaming/with_leaf_streaming take a
  StreamingHandler and wrap in HandlerKind::Stream for Subscription.
  Builder validates kind matches spec.op_type (mismatch = startup error)
- OperationRegistry::register() returns Result<(), String> with a clear
  mismatch message; all call sites updated to handle the Result
- invoke() matches on HandlerKind: Once -> existing path; Stream ->
  INVALID_OPERATION_TYPE error envelope (guards against silent
  truncation; invoke_streaming() added in a downstream task)
- OverlayOperationEnv::invoke_with_policy matches on HandlerKind:
  Once -> dispatch; Stream -> INVALID_OPERATION_TYPE (composition is
  request/response-only)
- Migrated every HandlerRegistration::new() construction site (~95)
  to wrap raw Handler in HandlerKind::Once(handler); the builder sites
  are handled by the builder-absorbs-wrapping change
- Updated two websocket subscription tests that relied on Subscription
  ops dispatching via invoke() to expect INVALID_OPERATION_TYPE
- Added unit tests for invoke/register validation and
  make_streaming_handler

crates/alknet-call/src/registry/env.rs

@@ -303,7 +303,9 @@ impl OperationEnv for PeerCompositeEnv {
 mod tests {
     use super::*;
     use crate::registry::context::CompositionAuthority;
-    use crate::registry::registration::{make_handler, HandlerRegistration, OperationProvenance};
+    use crate::registry::registration::{
+        make_handler, HandlerKind, HandlerRegistration, OperationProvenance,
+    };
     use crate::registry::spec::{AccessControl, OperationSpec, OperationType, Visibility};
     use alknet_core::auth::Identity;
     use alknet_core::types::Capabilities;
@@ -406,22 +408,24 @@ mod tests {
         scoped_env: Option<ScopedPeerEnv>,
     ) -> Arc<OperationRegistry> {
         let mut registry = OperationRegistry::new();
-        registry.register(HandlerRegistration::new(
-            OperationSpec::new(
-                name,
-                OperationType::Query,
-                spec_visibility,
-                serde_json::json!({}),
-                serde_json::json!({}),
-                vec![],
-                AccessControl::default(),
-            ),
-            handler,
-            OperationProvenance::Local,
-            composition_authority,
-            scoped_env,
-            Capabilities::new(),
-        ));
+        registry
+            .register(HandlerRegistration::new(
+                OperationSpec::new(
+                    name,
+                    OperationType::Query,
+                    spec_visibility,
+                    serde_json::json!({}),
+                    serde_json::json!({}),
+                    vec![],
+                    AccessControl::default(),
+                ),
+                HandlerKind::Once(handler),
+                OperationProvenance::Local,
+                composition_authority,
+                scoped_env,
+                Capabilities::new(),
+            ))
+            .unwrap();
         Arc::new(registry)
     }