fix: use model reasoning definitions and defaults when Copilot is used via OpenRouter

[KKKayleX]

Fixes #332152

As a result:

• Models that support extra effort tiers (e.g. xhigh, max) never surfaced
  them in the Thinking Effort picker — only low/medium/high were offered.
• The picker's default was derived from pickDefaultReasoningEffort (e.g.
  medium) instead of the model's own reasoning.default_effort.

Changes

In extensions/copilot/src/extension/byok/vscode-node/openRouterProvider.ts:

• Derive the supported effort list from reasoning.supported_efforts, falling
  back to ['low','medium','high'] when the model omits it, instead of always
  hard-coding that list.
• Forward reasoning.default_effort into the capabilities'
  defaultReasoningEffort so the picker can pre-select it.

[KKKayleX]

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[Copilot]

🟡 Changes recommended

The OpenRouter response type incorrectly requires a field that the implementation explicitly supports being omitted.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Updates OpenRouter model discovery to honor provider-defined reasoning effort levels and defaults.

Changes:

• Uses reasoning.supported_efforts with a standard fallback.
• Propagates reasoning.default_effort.
• Adds focused regression tests.

File summaries

File	Description
openRouterProvider.ts	Maps OpenRouter reasoning metadata into model capabilities.
test/openRouterProvider.spec.ts	Tests supported efforts, fallbacks, and defaults.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 2
• Review effort level: Balanced

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[KKKayleX]

Since #335272 was closed as a duplicate of #332152, this PR tracks #332152 instead.

This PR removes the hard-coded reasoning effort list and propagates reasoning.default_effort from OpenRouter model metadata.

Dmitriy Vasyura (@dmitrivMS) Vritant Bhardwaj (@vritant24)

[KKKayleX]

Thanks so much 🙏