feat(athena): add prepare_council_prompt tool for faster council launches

Athena saves the analysis prompt to a temp file once, then launches each
council member with a short "Read <path> for your instructions" prompt.
This eliminates repeated prompt text across N task calls while preserving
individual clickable task panes in the TUI.

src/shared/agent-tool-restrictions.ts

@@ -65,6 +65,7 @@ const AGENT_RESTRICTIONS: Record<string, Record<string, boolean>> = {
     call_omo_agent: false,
     switch_agent: false,
     background_wait: false,
+    prepare_council_prompt: false,
   },
 }