Remove 'prometheus' from PLAN_AGENT_NAMES so isPlanAgent() no longer
matches prometheus. The only remaining connection is model inheritance
via buildPlanDemoteConfig() in plan-model-inheritance.ts.
- Remove 'prometheus' from PLAN_AGENT_NAMES array
- Update self-delegation error message to say 'plan agent' not 'prometheus'
- Update tests: prometheus is no longer treated as a plan agent
- Update task permission: only plan agents get task tool, not prometheus