refactor: remove SPADE dependencies

Did not look at tests yet, this is a very non-final commit.

ref: N25B-300

src/control_backend/core/agent_system.py

@@ -0,0 +1,87 @@
+import asyncio
+import logging
+from abc import ABC, abstractmethod
+from dataclasses import dataclass, field
+from typing import Any
+
+# Central directory to resolve agent names to instances
+_agent_directory: dict[str, "BaseAgent"] = {}
+
+
+@dataclass
+class InternalMessage:
+    to: str
+    sender: str
+    body: str
+    thread: str | None = None
+    metadata: dict[str, Any] = field(default_factory=dict)
+
+
+class AgentDirectory:
+    @staticmethod
+    def register(name: str, agent: "BaseAgent"):
+        _agent_directory[name] = agent
+
+    @staticmethod
+    def get(name: str) -> "BaseAgent | None":
+        return _agent_directory.get(name)
+
+
+class BaseAgent(ABC):
+    logger: logging.Logger
+
+    def __init__(self, name: str):
+        self.name = name
+        self.jid = name  # present for backwards compatibility
+        self.inbox: asyncio.Queue[InternalMessage] = asyncio.Queue()
+        self._tasks: set[asyncio.Task] = set()
+        self._running = False
+
+        # Register immediately
+        AgentDirectory.register(name, self)
+
+    @abstractmethod
+    async def setup(self):
+        """Override this to initialize resources."""
+        pass
+
+    async def start(self):
+        """Starts the agent and its loops."""
+        self.logger.info(f"Starting agent {self.name}")
+        self._running = True
+        await self.setup()
+
+        # Start processing inbox
+        await self.add_background_task(self._process_inbox())
+
+    async def stop(self):
+        """Stops the agent."""
+        self._running = False
+        for task in self._tasks:
+            task.cancel()
+        self.logger.info(f"Agent {self.name} stopped")
+
+    async def send(self, message: InternalMessage):
+        target = AgentDirectory.get(message.to)
+        if target:
+            await target.inbox.put(message)
+        else:
+            self.logger.warning(f"Attempted to send message to unknown agent: {message.to}")
+
+    async def _process_inbox(self):
+        """Default loop: equivalent to a CyclicBehaviour receiving messages."""
+        while self._running:
+            msg = await self.inbox.get()
+            await self.handle_message(msg)
+
+    async def handle_message(self, msg: InternalMessage):
+        """Override this to handle incoming messages."""
+        raise NotImplementedError
+
+    async def add_background_task(self, coro):
+        """Helper to run cyclic behaviors."""
+        task = asyncio.create_task(coro)
+        self._tasks.add(task)
+        task.add_done_callback(self._tasks.discard)
+
+        # await asyncio.sleep(1)