Update darwin platform support from amd64 to arm64

[Copilot]

README.md incorrectly listed darwin amd64 as Tier 2 supported while marking darwin arm64 as unsupported. This is backwards—Apple Silicon (arm64) is now the standard Mac architecture.

Changes

• Mark arm64 Darwin as Tier 2 (supported)
• Mark amd64 Darwin as Not supported

This reflects Apple's transition away from Intel processors. The platform support table now accurately documents current hardware reality.

Original prompt

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This section details on the original issue you should resolve

<issue_title>bug: darwin support should be for arm64, not amd64</issue_title>
<issue_description>The README.md says we support darwin on amd64. This platform is mostly deprecated in favor of arm for darwin. I think the README.md is just out of date.</issue_description>

<agent_instructions>Review the entire repository and see if there is anything else darwin amd64 in any other documentation.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes bug: darwin support should be for arm64, not amd64 #4460

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[Copilot]

Pull Request Overview

This PR corrects the platform support documentation to reflect Apple's transition from Intel (amd64) to Apple Silicon (arm64) processors. The README.md previously incorrectly listed Intel Macs as supported while marking Apple Silicon as unsupported, which is backwards given current hardware reality.

Key changes:

• Mark arm64 Darwin as Tier 2 supported
• Mark amd64 Darwin as not supported

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[meaghanfitzgerald]

silly rabbit

[meaghanfitzgerald]

thanks @rkuris