fix(athena): prevent recursive council explosion — deny tool for bg tasks + dedup guard

Council members launched as agent='athena' got Athena's system prompt saying
'ALWAYS call athena_council first', plus the tool wasn't denied for bg athena
tasks. Each council member spawned 4 more → exponential explosion (47+ tasks).

Three fixes:
1. Deny athena_council in ATHENA_RESTRICTIONS (agent-tool-restrictions.ts)
   - Only affects background athena tasks (task-starter.ts)
   - Primary Athena (user-selected) still has access via permission field
2. Session-level dedup guard prevents re-calling while council is running
   - If Athena retries during long wait, returns 'already running'
3. Increase wait timeout from 2min to 10min (council members need time
   for real code analysis with Read/Grep/LSP)

src/shared/agent-tool-restrictions.ts

@@ -16,7 +16,7 @@ const EXPLORATION_AGENT_DENYLIST: Record<string, boolean> = {
 }
 
 const ATHENA_RESTRICTIONS = permissionToToolBooleans(
-  createAgentToolRestrictions(["write", "edit"]).permission
+  createAgentToolRestrictions(["write", "edit", "athena_council"]).permission
 )
 
 const AGENT_RESTRICTIONS: Record<string, Record<string, boolean>> = {