feat(athena): add dedicated council-member agent for multi-model council

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>

src/agents/builtin-agents.ts

@@ -14,6 +14,7 @@ import { createMomusAgent, momusPromptMetadata } from "./momus"
 import { createHephaestusAgent } from "./hephaestus"
 import { createSisyphusJuniorAgentWithOverrides } from "./sisyphus-junior"
 import { createAthenaAgent, ATHENA_PROMPT_METADATA } from "./athena/agent"
+import { createCouncilMemberAgent } from "./athena/council-member-agent"
 import type { AvailableCategory } from "./dynamic-agent-prompt-builder"
 import {
   fetchAvailableModels,
@@ -40,6 +41,7 @@ const agentSources: Partial<Record<BuiltinAgentName, AgentSource>> = {
   metis: createMetisAgent,
   momus: createMomusAgent,
   athena: createAthenaAgent,
+  "council-member": createCouncilMemberAgent,
   // Note: Atlas is handled specially in createBuiltinAgents()
   // because it needs OrchestratorContext, not just a model string
   atlas: createAtlasAgent as AgentFactory,