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/delegation.py

@@ -184,9 +184,7 @@ class Delegation:
         # a reason, and the next step is to talk about that reason.
         self._cancel = cancel or Cancel()
 
-    def run(
-        self, *, brief: str, branch: str, role: str = "delegate"
-    ) -> DelegationResult:
+    def run(self, *, brief: str, branch: str, role: str = "helper") -> DelegationResult:
         started_at = self._now()
         base_branch = self._git.current_branch()
         # Recorded before the branch exists, so a crash anywhere after this