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.

hermes_cli/tips.py

@@ -263,7 +263,7 @@ TIPS = [
     "Custom providers: save named endpoints in config.yaml under custom_providers.",
     "HERMES_EPHEMERAL_SYSTEM_PROMPT injects a system prompt that's never persisted to history.",
     "credential_pool_strategies supports fill_first, round_robin, least_used, and random rotation.",
-    "hermes login supports OAuth-based auth for Nous and OpenAI Codex providers.",
+    "hermes auth add nous or hermes auth add openai-codex sets up OAuth-based providers.",
     "The API server supports both Chat Completions and Responses API with server-side state.",
     "tool_preview_length: 0 in config shows full file paths in the spinner's activity feed.",
     "hermes status --deep runs deeper diagnostic checks across all components.",