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/config/schema/agent-names.ts

@@ -13,6 +13,7 @@ export const BuiltinAgentNameSchema = z.enum([
   "atlas",
   "sisyphus-junior",
   "athena",
+  "council-member",
 ])
 
 export const BuiltinSkillNameSchema = z.enum([
@@ -41,6 +42,7 @@ export const OverridableAgentNameSchema = z.enum([
   "multimodal-looker",
   "atlas",
   "athena",
+  "council-member",
 ])
 
 export const AgentNameSchema = BuiltinAgentNameSchema