fix: set agent_name via rtc_session decorator, revert CLI flag

AgentServer in livekit-agents 1.4.x does not support --agent-name CLI
flag. The agent_name must be set on @server.rtc_session() decorator.
Also reverts docker-compose.yml command back to plain python agent.py start.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

agent.py

@@ -27,7 +27,7 @@ def prewarm(proc: JobProcess):
 server.setup_fnc = prewarm
 
 
-@server.rtc_session()
+@server.rtc_session(agent_name=os.environ.get("AGENT_NAME", "matrix-ai"))
 async def entrypoint(ctx: JobContext):
     logger.info("Job received for room %s", ctx.job.room.name)