Claude Agent integration is visible but cannot be configured on self-hosted Sentry

### Self-Hosted Version

26.7.2

### CPU Architecture

x86_64

### Docker Version

Docker version 28.5.1, build e180ab8

### Docker Compose Version

Docker Compose version v2.40.3

### Machine Specification

- [x] My system meets the minimum system requirements of Sentry

### Installation Type

Upgrade

### Steps to Reproduce

1. Run self-hosted Sentry 26.7.2.
2. Go to Settings -> Integrations.
3. Open the Claude Agent integration.
4. Enter a valid Anthropic API key.
5. Try to install/configure the integration.
6. The setup fails with an error saying that CLAUDE_CODE_CLIENT_CLASS is not configured.

### Expected Result

The Claude Agent integration should either work on self-hosted Sentry with the required configuration documented, or it should not be displayed as an available integration if it is not supported on self-hosted installations.

### Actual Result

The Claude Agent integration is visible and allows me to start the configuration process, but after entering the Anthropic API key the setup fails with:

CLAUDE_CODE_CLIENT_CLASS is not configured. The Claude Code client is not available in this environment.

From the Sentry source code, CLAUDE_CODE_CLIENT_CLASS defaults to None, while the Claude Agent integration provider is still available in the UI.

It is unclear whether Claude Agent is supposed to be supported on self-hosted Sentry and, if it is, how CLAUDE_CODE_CLIENT_CLASS should be configured.

### Event ID

_No response_

Start by tracing how the Claude Agent integration provider is exposed in the self-hosted setup and where CLAUDE_CODE_CLIENT_CLASS defaults to None. Check whether self-hosted support is intended and identify the configuration path used after an Anthropic API key is entered. Done means the integration either configures successfully with documented settings or is no longer shown when unsupported.

Written by the indexing model from the issue text.