docs(providers): note that ANTHROPIC_API_KEY requires an API account, not a subscription (#1542)

* docs(providers): note that ANTHROPIC_API_KEY requires an API account, not a subscription

Anthropic subscription users authenticate via OAuth, not an API key,
causing a silent failure when creating the provider. Adds a Note callout
in the provider type table and quickstart guide directing subscription
users to generate an API key from console.anthropic.com.

Closes #620

* docs(providers): fix Note placement and remove subscription brand names

Move the Note callout in manage-providers.mdx to after the complete
provider type table so it does not break table rendering. Remove
subscription brand names from both Note callouts.

Author: mesutoezdil

docs/get-started/quickstart.mdx

@@ -60,6 +60,10 @@ The CLI prompts you to create a provider from local credentials.
 Type `yes` to continue.
 If `ANTHROPIC_API_KEY` is set in your environment, the CLI picks it up automatically.
 If not, you can configure it from inside the sandbox after it launches.
+
+<Note>
+`ANTHROPIC_API_KEY` is an API key from [console.anthropic.com](https://console.anthropic.com), not a subscription token. Subscription users must generate a separate API key.
+</Note>
 </Tab>
 
 <Tab title="OpenCode">

docs/sandboxes/manage-providers.mdx

@@ -255,6 +255,10 @@ The following provider types are supported.
 | `openai` | `OPENAI_API_KEY` | Any OpenAI-compatible endpoint. Set `--config OPENAI_BASE_URL` to point to the provider. Refer to [Inference Routing](/sandboxes/inference-routing). |
 | `opencode` | `OPENCODE_API_KEY`, `OPENROUTER_API_KEY`, `OPENAI_API_KEY` | OpenCode |
 
+<Note>
+`ANTHROPIC_API_KEY` is an API key from [console.anthropic.com](https://console.anthropic.com), not a subscription token. Subscription users must generate a separate API key from the Anthropic Console.
+</Note>
+
 <Tip>
 Use the `generic` type for any service not listed above. You define the
 environment variable names and values yourself with `--credential`.