fix(FN-3716): stabilize verification and role policy checks

- Add shared agent role policy helpers for implementation task detection and executor-role enforcement
- Provide a standardized role-mismatch error formatter for delegation and assignment paths
- Update test isolation leak detection to ignore ephemeral fusion-test-home-root temp directories while preserving baseline checks

Fusion-Task-Id: FN-3716

.changeset/FN-3716-executor-role-enforcement.md

@@ -0,0 +1,5 @@
+---
+"@runfusion/fusion": patch
+---
+
+Enforce executor-role assignment policy for implementation task delegation paths in the CLI and add an `override` escape hatch for intentional non-executor delegation.