ci: publish Intel macOS release binaries

[mchv]

Linked issue

• Fixes Bug: Installation failed - 404 error for darwin-x86_64 binary (v0.2.53) #147
• Related build: automate macOS codesign + notarization via GitHub Actions #94

Summary

• add a tagged/manual release workflow that publishes codedb-darwin-x86_64, codedb-darwin-arm64, and codedb-linux-x86_64
• build the Intel macOS binary on macos-15-intel so the installer target codedb-darwin-x86_64 is actually shipped
• make macOS codesigning configurable in build.zig instead of hardcoding a local Developer ID into every macOS build

Files touched

• build.zig
• .github/workflows/release-binaries.yml

Repro

Before:

• curl -I -fsSL https://codedb.codegraff.com/v0.2.53/codedb-darwin-x86_64 returns 404
• curl -fsSL https://github.com/justrach/codedb/releases/download/v0.2.53/checksums.sha256 has no codedb-darwin-x86_64 entry

After:

• pending GitHub Actions verification on this branch, since the fix is release automation and cannot be fully exercised locally in this environment
• workflow also supports workflow_dispatch so maintainers can backfill v0.2.53 after merge

Checks run

• git fetch upstream
• git rebase upstream/main
• ruby -e 'require "yaml"; YAML.load_file(".github/workflows/release-binaries.yml")'
• curl -I -fsSL https://ziglang.org/download/0.15.2/zig-x86_64-macos-0.15.2.tar.xz
• curl -I -fsSL https://ziglang.org/download/0.15.2/zig-aarch64-macos-0.15.2.tar.xz
• curl -I -fsSL https://ziglang.org/download/0.15.2/zig-x86_64-linux-0.15.2.tar.xz

Notes

• branch is rebased onto current upstream/main
• no generated files, lockfiles, or benchmark artifacts changed
• this submission matches CONTRIBUTING.md