Install eslint-plugin-package-json with recommended config

[Copilot]

• Install eslint-plugin-package-json as a dev dependency
• Add eslintPluginPackageJson.configs.recommended to eslint.config.js
• Fix package-json/require-exports — add exports field to package.json
• Fix package-json/require-files — add files field to package.json
• Fix package-json/require-sideEffects — add sideEffects: false to package.json
• Fix package-json/sort-collections — sort scripts lexicographically
• Add CSS entries to exports map so embetty-vue/dist/embetty-vue.css and embetty-vue/dist/embetty-vue.min.css remain importable
• Revert unrelated .vue file changes
• Remove .npmignore (superseded by files field)

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[Copilot]

Pull request overview

This PR introduces eslint-plugin-package-json and updates package.json metadata to satisfy the plugin’s recommended rules, while ensuring key published artifacts remain consumable.

Changes:

• Add eslint-plugin-package-json and enable its recommended flat config in eslint.config.js.
• Add exports, files, and sideEffects fields to package.json (and sort scripts lexicographically).
• Remove .npmignore in favor of the new files allowlist.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 1 comment.

File	Description
package.json	Adds exports map, publish files allowlist, sideEffects: false, and reorders scripts; adds new eslint plugin dev dependency.
package-lock.json	Locks new eslint-plugin-package-json dependency tree (including peer jsonc-eslint-parser).
eslint.config.js	Enables eslint-plugin-package-json recommended config in flat ESLint config.
.npmignore	Removed; publishing behavior is now controlled via files in package.json.

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