fix: handle None values in servers/agents config parsing

- Fix AttributeError when servers: or agents: is empty/None in config.yaml
- Use `or {}` pattern to safely handle None values
- Orchestrator CLI now starts correctly with minimal config

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

orchestrator/config.py

@@ -226,7 +226,8 @@ class Config:
     def _parse_servers(self) -> dict[str, ServerConfig]:
         """Parsea la sección servers."""
         servers = {}
-        for name, data in self._raw.get("servers", {}).items():
+        raw_servers = self._raw.get("servers") or {}
+        for name, data in raw_servers.items():
             if data:
                 servers[name] = ServerConfig(
                     name=name,
@@ -240,7 +241,8 @@ class Config:
     def _parse_agents(self) -> dict[str, AgentConfig]:
         """Parsea la sección agents."""
         agents = {}
-        for name, data in self._raw.get("agents", {}).items():
+        raw_agents = self._raw.get("agents") or {}
+        for name, data in raw_agents.items():
             if data:
                 agents[name] = AgentConfig(
                     name=name,