fix(athena): improve error extraction in council orchestrator

Replace String(result.reason) with proper instanceof Error check to produce clean error messages instead of [object Error] or full stack traces.

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

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

src/agents/athena/council-orchestrator.ts

@@ -46,7 +46,7 @@ export async function executeCouncil(input: CouncilExecutionInput): Promise<Coun
 
     failures.push({
       member,
-      error: `Launch failed: ${String(result.reason)}`,
+      error: `Launch failed: ${result.reason instanceof Error ? result.reason.message : String(result.reason)}`,
     })
   })