refactor(athena): remove athena_council from plugin wiring

Drop the barrel export, tool-registry registration, and agent-tool-restriction entry for the deleted athena_council tool.

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

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

src/shared/agent-tool-restrictions.ts

@@ -58,7 +58,6 @@ const AGENT_RESTRICTIONS: Record<string, Record<string, boolean>> = {
     edit: false,
     task: false,
     call_omo_agent: false,
-    athena_council: false,
   },
 }