feat(agent-zero): session memory + homelab project context

A2A server v2:
- Persistent conversation history per sender (20 msg limit)
- Homelab system prompt as default project context
- tasks/session/new and tasks/session/clear endpoints
- Session memory survives across multiple Zulip DMs

Adapter:
- Passes deterministic session_id per sender_name
- Conversations continue naturally without re-explaining context

agent-zero-zulip/src/agent_zero_zulip/adapter.py

@@ -272,8 +272,11 @@ class AgentZeroZulipAdapter:
                 await self._send_msg("private", str(sender_id), response[:MAX_ZULIP_MSG])
     
     async def _a2a_chat(self, sender_name: str, message: str) -> Optional[str]:
-        """Send message to Agent Zero via local A2A protocol."""
+        """Send message to Agent Zero via local A2A protocol with session memory."""
         try:
+            # Use sender_name as stable session key so conversation persists
+            session_id = f"zulip-{sender_name.lower().replace(' ', '-')}"
+            
             a2a_payload = {
                 "jsonrpc": "2.0",
                 "method": "tasks/send",
@@ -282,6 +285,9 @@ class AgentZeroZulipAdapter:
                     "message": {
                         "role": "user",
                         "parts": [{"text": f"[Zulip DM from {sender_name}]: {message}"}]
+                    },
+                    "metadata": {
+                        "session_id": session_id
                     }
                 },
                 "id": 1