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/client/from_call.rs

@@ -19,7 +19,9 @@ use crate::client::AdapterError;
 use crate::protocol::connection::CallConnection;
 use crate::protocol::wire::ResponseEnvelope;
 use crate::registry::context::OperationContext;
-use crate::registry::registration::{Handler, HandlerRegistration, OperationProvenance};
+use crate::registry::registration::{
+    Handler, HandlerKind, HandlerRegistration, OperationProvenance,
+};
 use crate::registry::spec::{
     AccessControl, ErrorDefinition, OperationSpec, OperationType, Visibility,
 };
@@ -128,7 +130,7 @@ fn build_bundles(
         );
         bundles.push(HandlerRegistration::new(
             spec,
-            handler,
+            HandlerKind::Once(handler),
             OperationProvenance::FromCall,
             None,
             None,
@@ -549,7 +551,7 @@ mod tests {
         );
         let reg = HandlerRegistration::new(
             spec,
-            handler,
+            HandlerKind::Once(handler),
             OperationProvenance::FromCall,
             None,
             None,