fix: add AgentRegistry.get_all() method

Routers calling /registry/agents raised AttributeError because
get_all() was not defined. Added method returning all registered
agents with active status, capabilities and instance flags.

agent_service/agents/registry.py

@@ -26,6 +26,18 @@ class AgentRegistry:
         return [{'agent_key': k, 'capabilities_summary': self._capabilities.get(k, '')}
                 for k in self._active]
 
+    async def get_all(self):
+        """Return all registered agents with active status and capabilities."""
+        return [
+            {
+                'agent_key': k,
+                'active': k in self._active,
+                'capabilities_summary': self._capabilities.get(k, ''),
+                'has_instance': k in self._agents,
+            }
+            for k in self._agents
+        ]
+
     async def is_active(self, agent_key):
         return agent_key in self._active