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).

.env.example

@@ -53,10 +53,6 @@ MINIMAX_CN_API_KEY=
 # Get at: https://firecrawl.dev/
 FIRECRAWL_API_KEY=
 
-# Nous Research API Key - Vision analysis and multi-model reasoning
-# Get at: https://inference-api.nousresearch.com/
-NOUS_API_KEY=
-
 # FAL.ai API Key - Image generation
 # Get at: https://fal.ai/
 FAL_KEY=