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.example.yaml

@@ -25,8 +25,8 @@ llm:                                  # L9: LiteLLM is the only LLM destination
 roles:                                # L9: role -> LiteLLM model alias
   executor: qwen3.8-27b         # the local tier: best executor in the benchmark (PR #55)
   planner: claude-opus-5-5      # high-end judgement: plans a weaker executor follows
-  delegate: claude-opus-5-5     # takes over what the executor got stuck on
-  consultant: claude-haiku-4-5  # one question at a time, no tools: cheap is enough
+  helper: claude-opus-5-5     # takes over what the executor got stuck on
+  expert: claude-haiku-4-5  # one question at a time, no tools: cheap is enough
 
 matrix:                               # L5
   homeserver: https://matrix.example