feat: add Claude Opus 4.6 model to playground

[veeceey]

Summary

Adds Claude Opus 4.6 (claude-opus-4-6) support to the Phoenix playground and cost tracking, addressing the request in #11270.

Changes

• Playground (Anthropic provider): Register claude-opus-4-6 with AnthropicReasoningStreamingClient, which provides extended thinking parameter support
• Playground (AWS Bedrock provider): Register anthropic.claude-opus-4-6-v1 with BedrockStreamingClient
• Cost tracking: Add claude-opus-4-6 entry to model_cost_manifest.json with correct pricing ($5/$25 per MTok input/output, plus cache read/write rates matching Opus 4.5)

Why this approach

Claude Opus 4.6 supports extended thinking (like all Claude 4.x models), so it is registered with AnthropicReasoningStreamingClient rather than the base AnthropicStreamingClient. This ensures the thinking invocation parameter is available in the playground UI.

The model does not have a separate dated version ID -- Anthropic uses claude-opus-4-6 as both the alias and the API ID (source).

Pricing is sourced from Anthropic's pricing page.

Note on scope

This PR covers the core integration (model registration + cost tracking). The more advanced features mentioned in #11270 (adaptive thinking toggle, effort parameter, compaction API, data residency controls) would require more significant UI and backend changes and are better suited for follow-up work.

Test plan

• Verify claude-opus-4-6 appears in the Anthropic provider model dropdown
• Verify anthropic.claude-opus-4-6-v1 appears in the AWS Bedrock provider model dropdown
• Verify the thinking (extended thinking) invocation parameter is available when Opus 4.6 is selected
• Verify cost tracking correctly calculates costs for Opus 4.6 spans

Closes #11270

---

Note

Low Risk
Adds new model identifiers and pricing metadata without changing core request/streaming logic; risk is limited to incorrect model routing or cost calculations if the IDs/rates are wrong.

Overview
Adds Claude Opus 4.6 model selection support in the playground by registering claude-opus-4-6 under the Anthropic reasoning client (enabling the thinking parameter) and anthropic.claude-opus-4-6-v1 under the AWS Bedrock client.

Updates cost tracking by adding claude-opus-4-6 (and a dated variant) to model_cost_manifest.json with token pricing (input/output plus cache read/write rates) so spans can be costed correctly.

^{Written by Cursor Bugbot for commit f576a41. This will update automatically on new commits. Configure here.}

[github-actions]

CLA Assistant Lite bot All contributors have signed the CLA ✍️ ✅

[veeceey]

I have read the CLA Document and I hereby sign the CLA

[veeceey]

Addressed the Cursor Bugbot feedback: added the missing :0 version suffix to anthropic.claude-opus-4-6-v1 to match the pattern used by all other Anthropic Bedrock model IDs (e.g., anthropic.claude-opus-4-5-20251101-v1:0). Fixed in 97fd31a.

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Bugbot Autofix is OFF. To automatically fix reported issues with Cloud Agents, enable Autofix in the Cursor dashboard.}

[RogerHYang]

Thank you for your contribution!