feat(athena): register council members as task-callable subagents

Each council member from config is now registered as a named agent (e.g. 'Council: Claude Opus 4.6') via registerCouncilMemberAgents(). Adds humanizeModelId() to derive friendly display names from model IDs. Athena's prompt gets the member list appended so it can call task(subagent_type=...) for each.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/plugin-handlers/agent-config-handler.ts

@@ -154,6 +154,7 @@ export async function applyAgentConfig(params: {
     }
   );
 
+  const athenaCouncilConfig = params.pluginConfig.agents?.athena?.council
   const builtinAgents = await createBuiltinAgents(
     migratedDisabledAgents,
     params.pluginConfig.agents,
@@ -168,6 +169,7 @@ export async function applyAgentConfig(params: {
     disabledSkills,
     useTaskSystem,
     disableOmoEnv,
+    athenaCouncilConfig,
   );
 
   const disabledAgentNames = new Set(