Bug: AWS-Anthropic custom provider sends deprecated Anthropic request fields

## Bug: AWS-Anthropic custom provider sends deprecated Anthropic request fields

### Environment
- GitHub Copilot App: 1.0.80
- OS: macOS
- Provider type: AWS-Anthropic
- Wire API: Anthropic Messages
- Model display name: claude-opus-4-8 / claude-opus-5
- Wire model sent to provider: anthropic.claude-opus-4-8 / anthropic.claude-opus-5
- Custom base URL: https:///anthropic
- Header: anthropic-version: 2023-06-01

### Steps to reproduce
1. Configure an AWS-Anthropic custom provider with an Anthropic Messages-compatible endpoint.
2. Configure Claude Opus 4.8 or Opus 5 using an `anthropic.` wire model ID.
3. Send a simple prompt such as “你好”.

### Actual result
The GitHub Copilot App sends legacy request fields. The upstream rejects them with:

- `400 temperature is deprecated for this model`
- `400 "thinking.type.enabled" is not supported for this model. Use "thinking.type.adaptive" and "output_config.effort" to control thinking behavior.`

### Expected result
For current Claude models, the AWS-Anthropic provider should omit deprecated sampling fields (`temperature`, `top_p`, `top_k`) and use the current thinking protocol:
`thinking.type: "adaptive"` with `output_config.effort`, or provide a per-model capability/protocol setting.

### Impact
The Custom endpoint provider cannot be used as a workaround because it only offers OpenAI-compatible Completions/Responses wire APIs, not Anthropic Messages. This prevents use of current Claude Bedrock models through a custom Anthropic endpoint without external request rewriting.

### Evidence
Attached screenshots show:
- the AWS-Anthropic provider and model configuration;
- real Copilot request failures;
- request IDs from the failed requests.

---
| Field | Value |
| --- | --- |
| App version | 1.1.14 |
| OS | macOS 15.7.5 |
| Theme | GitHub |
| Path | /chat |
| Tenure | Day 6 (Week 1) |

No files or tests are named. Start by tracing the AWS-Anthropic custom provider's Anthropic Messages request path and its model capability handling, then reproduce the request with the listed Claude wire model IDs. Done means current models no longer receive deprecated sampling fields and use the expected adaptive thinking protocol, with coverage for the reported configuration.

Written by the indexing model from the issue text.