docs(anthropic): clarify OAuth uses Claude Pro/Max subscription usage (#17399)

Users have been asking what they're billed for when they authenticate
Anthropic via OAuth in Hermes. Clarify in the provider docs that OAuth
routes through Anthropic's Claude Code subscription path — consuming
the extra Claude Code usage included with their Pro or Max plan — and
that an ANTHROPIC_API_KEY is pay-per-token against that key's org
instead.

Touches:
- integrations/providers.md: new info admonition in Anthropic (Native)
  section, plus provider-table row.
- user-guide/features/credential-pools.md: OAuth comment line.
- reference/environment-variables.md: Provider Auth (OAuth) intro.
- getting-started/quickstart.md: provider-picker table row.

website/docs/getting-started/quickstart.md

@@ -70,7 +70,7 @@ Good defaults:
 |----------|-----------|---------------|
 | **Nous Portal** | Subscription-based, zero-config | OAuth login via `hermes model` |
 | **OpenAI Codex** | ChatGPT OAuth, uses Codex models | Device code auth via `hermes model` |
-| **Anthropic** | Claude models directly (Pro/Max or API key) | `hermes model` with Claude Code auth, or an Anthropic API key |
+| **Anthropic** | Claude models directly — Pro/Max subscription (uses your included Claude Code usage) or API key | `hermes model` → OAuth login, or an Anthropic API key |
 | **OpenRouter** | Multi-provider routing across many models | Enter your API key |
 | **Z.AI** | GLM / Zhipu-hosted models | Set `GLM_API_KEY` / `ZAI_API_KEY` |
 | **Kimi / Moonshot** | Moonshot-hosted coding and chat models | Set `KIMI_API_KEY` |