feat(agent-zero): Zulip adapter with A2A protocol for kagentz

New project: agent-zero-zulip/ — direct Zulip integration for Agent Zero
agents using A2A protocol internally.

Architecture:
  kagentz (CT 105) ┌──────────────────────┐
                    │ Zulip Adapter  ◄──►  │ Agent Zero
                    │ polls Zulip    A2A   │ Docker container
                    │ port 8001            │
                    └──────────────────────┘

- adapter.py: Zulip event queue poller + A2A client
- No intermediate bridge — direct kagentz ↔ Zulip
- Heartbeat, reconnection, placeholder→edit streaming
- Designed for re-use: scottdenya, future Agent Zero agents

agent-zero-zulip/requirements.txt

@@ -0,0 +1 @@
+httpx>=0.27.0