fix(athena): write council prompt to .sisyphus/tmp/, switch to allow-list permissions

Council members now use an allow-list (read, grep, glob, lsp_*, ast_grep_search)
instead of a deny-list. Prompt file moved from /tmp/ to .sisyphus/tmp/ so no
external_directory permission is needed. COUNCIL_MEMBER_PROMPT is included in
the temp file for self-contained council member instructions.

src/agents/AGENTS.md

@@ -35,7 +35,7 @@ Agent factories following `createXXXAgent(model) → AgentConfig` pattern. Each
 | Atlas | task, call_omo_agent |
 | Momus | write, edit, task |
 | Athena | write, edit, call_omo_agent |
-| Council-Member | write, edit, task, call_omo_agent, switch_agent, background_wait, prepare_council_prompt |
+| Council-Member | ALL except read, grep, glob, lsp_*, ast_grep_search (allow-list) |
 
 ## STRUCTURE