iter-30: drop x86_64-apple-darwin from CI and release

[ractive]

Summary

• Drop the x86_64-apple-darwin / macos-13 matrix entry from ci.yml and release.yml — GitHub's macos-13 runner pool is wound down and jobs sit indefinitely in "Waiting for a runner".
• Drop the on_intel macOS block (and SHA_MACOS_X86) from the Homebrew formula heredoc.
• README: add the "Intel Mac users → cargo install" hint, mirroring the sibling hyalo project.

Apple Silicon (aarch64-apple-darwin on macos-latest) still proves macOS builds and tests pass; Intel Mac users get covered by cargo install hoppy from crates.io.

Test plan

• CI run on this PR: no perpetually-queued macos-13 job; all five remaining matrix entries (linux x86_64, linux aarch64 cross, darwin aarch64, windows x86_64, windows aarch64) report green.
• On the next release, confirm the brew formula renders without an on_intel macOS block and brew install ractive/tap/hoppy succeeds on Apple Silicon.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Added support for ARM64-based Linux systems

• Documentation

  • Updated installation instructions: Homebrew bottles now available for Apple Silicon and ARM64 Linux only. Intel Mac users should use cargo install

[coderabbitai]

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Free

Run ID: 7d0b2d0a-57b0-49de-9a91-12a372711681

📥 Commits

Reviewing files that changed from the base of the PR and between 24d0230 and f2cb5de.

📒 Files selected for processing (4)

• .github/workflows/ci.yml
• .github/workflows/release.yml
• README.md
• hoppy-knowledgebase/iterations/iteration-30-drop-x86-macos.md

💤 Files with no reviewable changes (1)

• .github/workflows/ci.yml

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📝 Walkthrough

Walkthrough

This PR removes Intel macOS (x86_64-apple-darwin) as a CI build and release target, adds Linux ARM64 (aarch64-unknown-linux-gnu) cross-compilation support to CI, updates the release workflow and Homebrew formula generation accordingly, and clarifies installation instructions for Intel Mac users in the README.

Changes

macOS Intel Sunset and Linux ARM64 Addition

Layer / File(s)	Summary
Iteration Specification hoppy-knowledgebase/iterations/iteration-30-drop-x86-macos.md	Planning document for Iteration 30 outlines the decision to drop Intel macOS, specifies workflow changes, defines verification criteria, and documents acceptance checklist.
CI Build Matrix .github/workflows/ci.yml	CI workflow build matrix removes x86_64-apple-darwin entry and adds aarch64-unknown-linux-gnu on ubuntu-latest with cross-compilation enabled.
Release Packaging & Homebrew Formula .github/workflows/release.yml	Release workflow drops x86_64-apple-darwin from build matrix, removes SHA_MACOS_X86 checksum variable from validation loop, and removes on_intel stanza from generated Homebrew formula's macOS section.
User-Facing Documentation README.md	Adds note in installation section clarifying that Homebrew bottles are available only for Apple Silicon and directing Intel Mac users to cargo install.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 The Intel Mac, once proud and grand,
Now hands off to Apple Silicon's land.
Linux ARM joins the build brigade,
While cargo install saves the day, well played!

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Note

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