refactor(agents): add prometheus agent and normalize agent key lookups

- Add 'prometheus' to BuiltinAgentNameSchema enum
- Update delegate_task parameter names in documentation (agent → subagent_type, background → run_in_background)
- Make agent name comparison case-insensitive in Atlas hook
- Implement case-insensitive agent config lookup in shared utilities
- Relax type signature for disabled agents parameter

🤖 Generated with assistance of OhMyOpenCode

src/agents/utils.ts

@@ -139,7 +139,7 @@ function mapScopeToLocation(scope: SkillScope): AvailableSkill["location"] {
 }
 
 export async function createBuiltinAgents(
-  disabledAgents: BuiltinAgentName[] = [],
+  disabledAgents: string[] = [],
   agentOverrides: AgentOverrides = {},
   directory?: string,
   systemDefaultModel?: string,