docs(auth): replace stale 'hermes login' references with 'hermes auth add'

'hermes login' was removed (the command now just prints a deprecation
message and exits). The bundled hermes-agent SKILL.md, in-code error
messages, the tip rotation, the proxy adapters, and the docs site
still pointed agents and users at the dead command — so models loading
the skill kept running 'hermes login --provider openai-codex' and
getting a dead-end print.

Replacements use the canonical 'hermes auth add <provider>' surface
(or bare 'hermes auth' for the interactive manager).

Files:
- skills/autonomous-ai-agents/hermes-agent/SKILL.md (+ regenerated docs page)
- hermes_cli/tips.py (tip rotation)
- agent/google_oauth.py (gemini-cli error message)
- agent/conversation_loop.py (nous re-auth troubleshooting line)
- agent/credential_sources.py (docstring)
- hermes_cli/proxy/cli.py + hermes_cli/proxy/adapters/nous_portal.py (proxy auth hints)
- tests/hermes_cli/test_proxy.py (updated assertions)
- website/docs/reference/faq.md, website/docs/user-guide/features/subscription-proxy.md
- zh-Hans i18n mirrors for the above

'hermes logout' is still a live command and is left untouched.
The 'hermes login' stub in hermes_cli/auth.py:login_command() and
the cli-commands.md 'Deprecated' rows are intentionally kept as
the discoverable deprecation surface.

tests/hermes_cli/test_proxy.py

@@ -207,7 +207,7 @@ def test_nous_adapter_retry_credential_skips_opaque_bearer(tmp_path, monkeypatch
 def test_nous_adapter_get_credential_raises_when_not_logged_in(tmp_path, monkeypatch):
     monkeypatch.setenv("HERMES_HOME", str(tmp_path))
     adapter = NousPortalAdapter()
-    with pytest.raises(RuntimeError, match="hermes login nous"):
+    with pytest.raises(RuntimeError, match="hermes auth add nous"):
         adapter.get_credential()
 
 
@@ -784,4 +784,4 @@ def test_cmd_proxy_start_refuses_when_unauthenticated(capsys, tmp_path, monkeypa
     rc = cmd_proxy_start(args)
     assert rc == 2
     err = capsys.readouterr().err
-    assert "hermes login nous" in err
+    assert "hermes auth add nous" in err