Rename the delegate and consultant roles to helper and expert

Architecture L9's role names, for the two roles with a direct
counterpart: the delegation role is now 'helper' and the ask_expert role
'expert', in RoleMap, configuration (roles.helper, roles.expert),
recorded events and tests. 'planner' and 'executor' stay distinct for
now; they become 'driver' when the new loop merges them (Development
Plan M2.3).

Configurations must rename their keys: nisse-dev.example.yaml and
tests/integration/nisse-test.yaml are updated here.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPQ14L3LikyefCMFBqEbKE

nisse-dev/src/nisse_dev/executor.py

@@ -165,7 +165,7 @@ class LLMExecutor:
             # that it is circling and should get on with the work or fail.
             return ToolOutcome(str(exc), success=False)
         except LLMError as exc:
-            return ToolOutcome(f"the consultant did not answer: {exc}", success=False)
+            return ToolOutcome(f"the expert did not answer: {exc}", success=False)
 
     def _scope(self) -> tuple[str | None, int]:
         """The approved plan, and where this milestone's events begin.