npm installer pulls 41 transitive dependencies via axios — consider bundled binary approach

## Problem

The npm installer generated by cargo-dist uses a JS downloader approach that brings in 5 direct runtime dependencies:

- `axios` (+ `axios-proxy-builder`)
- `console.table` (unused — already a Node built-in since v10, see #2224)
- `detect-libc`
- `rimraf`

This results in **41 packages installed** for what is fundamentally a single static binary. For comparison, tools like esbuild, swc, and biome use platform-specific optional dependencies (`@esbuild/linux-x64`, etc.) that contain the binary directly — zero runtime JS dependencies, no postinstall download step.

```
$ npm install @silafood/runsteps@0.1.0
41 packages installed
```

## Suggestion

Consider offering a bundled binary strategy (as described in #450) where:

1. Platform-specific packages (`@scope/tool-linux-x64`, `@scope/tool-darwin-arm64`, etc.) each contain the prebuilt binary
2. The root package lists them as `optionalDependencies`
3. npm/bun/pnpm automatically picks the right one for the platform

This eliminates:
- All 5 runtime dependencies (axios, detect-libc, rimraf, console.table, axios-proxy-builder)
- The postinstall download step (binary is already in the package)
- Network failures during install (no GitHub fetch at install time)
- The 41-package dependency tree

## Current workaround

Using the shell installer (`curl | sh`) or Homebrew instead of npm, since those have zero dependencies.

## Environment

- cargo-dist 0.31.0
- `installers = ["shell", "npm", "homebrew"]`

Start with cargo-dist's generated npm installer and the installer configuration shown in the issue, then read the bundled binary strategy described in #450. Determine how platform-specific packages, optionalDependencies, and package contents should be represented; done means npm installs the matching binary without runtime dependencies, postinstall downloads, or GitHub network access.

Written by the indexing model from the issue text.