fix(athena): address 9 council-audit findings — dead code, bugs, and hardening

Fixes from multi-model council audit (7 members, 19 findings, 9 selected):

- Use parseModelString() for cross-provider Anthropic thinking config (#3)
- Update stale AGENTS.md athena directory listing (#4)
- Replace prompt in appendMissingCouncilPrompt instead of appending (#5)
- Extract duplicated session cleanup logic in agent-switch hook (#6)
- Surface skipped council members when >=2 valid members exist (#9)
- Expand fallback handoff regex with negation guards (#11)
- Remove dead council-member agent from agentSources and tests (#12)
- Make runtime council member duplicate check case-insensitive (#14)
- Fix false-positive schema tests by adding required name field (#18)

src/plugin/tool-execute-before.ts

@@ -41,7 +41,7 @@ export function createToolExecuteBeforeHandler(args: {
 
     const tasks = backgroundManager.getTasksByParentSession(sessionID)
     return tasks.some((task) =>
-      (task.agent === "council-member" || task.agent.startsWith(COUNCIL_MEMBER_KEY_PREFIX)) &&
+      task.agent.startsWith(COUNCIL_MEMBER_KEY_PREFIX) &&
       (task.status === "pending" || task.status === "running")
     )
   }