fix: register shareman recovery interface in ActiveContext

Add missing shareman->RegisterRecoveryInterface() call in
ActiveContext::Start() and corresponding UnregisterRecoveryInterface()
in Stop().

Without this, completed sig share sessions are only cleaned up via the
5-second Cleanup() interval instead of promptly via
HandleNewRecoveredSig. Under CI load with frozen mocktime, this
manifests as flaky test failures in feature_llmq_signing.py and
interface_zmq_dash.py.

The registration was likely dropped during the sig share refactoring
that split share management into a separate shareman object.

Closes dashpay#7243

Author: thepastaclaw

src/active/context.cpp

@@ -70,6 +70,7 @@ void ActiveContext::Start(CConnman& connman, PeerManager& peerman, int16_t worke
     cl_signer->Start();
     cl_signer->RegisterRecoveryInterface();
     is_signer->RegisterRecoveryInterface();
+    shareman->RegisterRecoveryInterface();
 
     RegisterValidationInterface(cl_signer.get());
 }
@@ -78,6 +79,7 @@ void ActiveContext::Stop()
 {
     UnregisterValidationInterface(cl_signer.get());
 
+    shareman->UnregisterRecoveryInterface();
     is_signer->UnregisterRecoveryInterface();
     cl_signer->UnregisterRecoveryInterface();
     cl_signer->Stop();