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.

agent/conversation_loop.py

@@ -2218,7 +2218,7 @@ def run_conversation(
                         print(f"{agent.log_prefix}   Response: {_body_text}")
                     print(f"{agent.log_prefix}   Most likely: Portal OAuth expired, account out of credits, or agent key revoked.")
                     print(f"{agent.log_prefix}   Troubleshooting:")
-                    print(f"{agent.log_prefix}     • Re-authenticate: hermes login --provider nous")
+                    print(f"{agent.log_prefix}     • Re-authenticate: hermes auth add nous")
                     print(f"{agent.log_prefix}     • Check credits / billing: https://portal.nousresearch.com")
                     print(f"{agent.log_prefix}     • Verify stored credentials: {_dhh}/auth.json")
                     print(f"{agent.log_prefix}     • Switch providers temporarily: /model <model> --provider openrouter")