Modernize build tooling and drop ES5 output

[mschroeder]

Summary

Modernize the package build and remove the ES5 bundle. This is a breaking packaging/runtime change; the package version is bumped to 3.0.0.

Changes

• Require Node.js >=22.12.0.
• Replace the Rollup/Babel build with Vite 8/Rolldown.
• Publish modern ESM, CommonJS, and browser-global IIFE bundles, with minified variants and source maps.
• Preserve direct script/CDN use and the global ICAL API for modern browsers; remove the ES5-era compatibility promise.
• Generate TypeScript declarations directly with tsc.
• Update package exports, release assets, and README examples.
• Extract Mocha and JSDoc configuration into dedicated configs and a build script.

Validation

• npm run build
• npm test
• npm run test-browser (Chromium, Firefox, WebKit)
• npm run lint
• npm ci --dry-run
• npm audit --omit=optional
• npm pack --dry-run