Replace oracle as the agent for council background tasks with a purpose-built
council-member agent. This avoids coupling to oracle's config/prompt and provides
proper read-only tool restrictions (deny write, edit, task, athena_council).
- New council-member-agent.ts with analysis-oriented system prompt
- Registered in agentSources (hidden from Sisyphus delegation table)
- Added to type system, Zod schemas, display names, tool restrictions
- Minimal model fallback (always overridden per council member at launch)
- Council orchestrator now launches members as council-member agent
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
- add athena to built-in and overridable agent name schemas
- extend BuiltinAgentName with athena for config-level recognition
- make builtin agent source maps partial until athena runtime registration lands
Sisyphus-Junior was missing from BuiltinAgentName type, agentSources map,
barrel exports, and AGENT_MODEL_REQUIREMENTS. This caused type inconsistencies
and prevented model-fallback hooks from working for sisyphus-junior sessions.
Closescode-yeongyu/oh-my-openagent#1697