refactor(delegate): drop dead default_toolsets from CLI default config

delegation.default_toolsets was declared in cli.py's CLI_CONFIG default
dict and documented in cli-config.yaml.example, but never read: none of
tools/delegate_tool.py, _load_config(), or any call site ever looked it
up. The live fallback is the DEFAULT_TOOLSETS module constant at
tools/delegate_tool.py:101, which stays as-is.

hermes_cli/config.py's DEFAULT_CONFIG["delegation"] already omits the
key — this commit aligns cli.py with that.

Adds a regression test in tests/hermes_cli/test_config_drift.py so a
future refactor that re-adds the key without wiring it up to
_load_config() fails loudly.

Part of Initiative 2 / M0.5.

cli.py

@@ -371,7 +371,6 @@ def load_cli_config() -> Dict[str, Any]:
         },
         "delegation": {
             "max_iterations": 45,  # Max tool-calling turns per child agent
-            "default_toolsets": ["terminal", "file", "web"],  # Default toolsets for subagents
             "model": "",       # Subagent model override (empty = inherit parent model)
             "provider": "",    # Subagent provider override (empty = inherit parent provider)
             "base_url": "",    # Direct OpenAI-compatible endpoint for subagents