Add Linux ARM64 platform binary

Summary

Adds a linux-arm64 build target and @d3k/linux-arm64 platform package, mirroring the existing darwin-arm64 / linux-x64 / windows-x64 packages, so d3k installs and runs on Linux ARM64.

This makes it possible to run d3k inside native-arm64 VS Code devcontainers on Apple Silicon Macs.

Changes

• Add { os: "linux", arch: "arm64" } to the binary build matrix (scripts/build-binaries.ts)
• Register linux-arm64 → @d3k/linux-arm64 in the platform wrapper (bin/dev3000)
• Add the @d3k/linux-arm64 platform package and wire it into optionalDependencies + bun.lock
• Extend the canary/release scripts and release workflow to build and publish the new package

Test plan

• Lint passes
• TypeScript passes
• Tests pass
• Cross-compiled bun-linux-arm64 binary runs in a native linux/arm64 container (--version / --help)