chore: remove all NOUS_API_KEY references

NOUS_API_KEY is unused — vision tools use OPENROUTER_API_KEY or Nous
Portal OAuth (auth.json), and MoA tools use OPENROUTER_API_KEY.

Removed from:
- hermes_cli/config.py: api_keys allowlist for config set routing
- .env.example: example env file entry and comment
- tests/hermes_cli/test_set_config_value.py: parametrize test data
- tests/integration/test_web_tools.py: updated comments and log
  messages to reference 'auxiliary LLM provider' instead of NOUS_API_KEY

No HECATE references found in codebase (already cleaned up).

tests/hermes_cli/test_set_config_value.py

@@ -38,7 +38,6 @@ class TestExplicitAllowlist:
         "OPENROUTER_API_KEY",
         "OPENAI_API_KEY",
         "ANTHROPIC_API_KEY",
-        "NOUS_API_KEY",
         "WANDB_API_KEY",
         "TINKER_API_KEY",
         "HONCHO_API_KEY",