feat: unified /model and /provider into single view

Both /model and /provider now show the same unified display:

  Current: anthropic/claude-opus-4.6 via OpenRouter

  Authenticated providers & models:
    [openrouter] ← active
      anthropic/claude-opus-4.6 ← current
      anthropic/claude-sonnet-4.5
      ...
    [nous]
      claude-opus-4-6
      gemini-3-flash
      ...
    [openai-codex]
      gpt-5.2-codex
      gpt-5.1-codex-mini
      ...

  Not configured: Z.AI / GLM, Kimi / Moonshot, ...

  Switch model:    /model <model-name>
  Switch provider: /model <provider>:<model-name>
  Example: /model nous:claude-opus-4-6

Users can see all authenticated providers and their models at a glance,
making it easy to switch mid-conversation.

Also added curated model lists for Nous Portal and OpenAI Codex to
hermes_cli/models.py.

tests/test_cli_model_command.py

@@ -93,8 +93,8 @@ class TestModelCommand:
         output = capsys.readouterr().out
         assert "anthropic/claude-opus-4.6" in output
         assert "OpenRouter" in output
-        assert "Available models" in output
-        assert "provider:model-name" in output
+        assert "Authenticated providers" in output or "Switch model" in output
+        assert "provider" in output and "model" in output
 
     # -- provider switching tests -------------------------------------------