chore: migrate build system from webpack 4 to Vite 6

[Copilot]

Replaces the webpack 4 build pipeline (requiring NODE_OPTIONS="--openssl-legacy-provider" on Node 17+) with Vite 6.4.2, which works natively with modern Node.js and produces faster builds.

Key changes

• vite.config.mjs — new Vite config in UMD library mode:

  • Custom resolve-src plugin replicates webpack's resolve.modules: ['./src'], preserving bare imports like import { ... } from "storage.js"
  • Externals (jquery → jQuery, knockout → ko, filepond → FilePond) carried over unchanged
  • BUILD_MIN=true env var toggles minification and selects output filename (blockpy.js vs blockpy.min.js)
  • CSS extracted to dist/blockpy.css; inline source maps retained

• package.json:

  • build: vite build --config vite.config.mjs && cross-env BUILD_MIN=true vite build --config vite.config.mjs
  • dev: vite build --watch --config vite.config.mjs
  • Removed: webpack, webpack-cli, babel-loader, eslint-loader, css-loader, mini-css-extract-plugin, @babel/core, @babel/preset-env, yargs, path
  • Added: vite@6.4.2, cross-env@10.1.0 (cross-platform env var syntax)

• Removed: webpack.config.js, .babelrc

Output (unchanged structure)

File	Description
dist/blockpy.js	Unminified UMD bundle
dist/blockpy.min.js	Minified UMD bundle
dist/blockpy.css	Extracted styles