PR Title: chore!: modernize toolchain (Vite 7, Vitest 3), migrate ESLint to flat config, add Prettier, and update Sass to module API

[anilkumarthakur60]

Context

This PR upgrades the dev toolchain and tidies up configuration so the package builds cleanly on modern Node (≥20), reduces maintenance overhead, and silences upcoming deprecations (Sass @import).

Summary

• Upgrade build/test stack:

  • Vite → 7.x, @vitejs/plugin-vue → 6.x
  • Vitest → 3.x with @vitest/coverage-v8
  • TypeScript 5.9, Vue 3.5, Sass 1.91

• ESLint 9 flat config: replace legacy .eslintrc with eslint.config.mjs (and eslint.config.ts example), update scripts.

• Prettier: add strict .prettierrc.json + broadened .prettierignore; format codebase (HTML/JS/README).

• Sass modules: move away from deprecated @import in src/styles/index.scss to the module system (@forward barrel).

• Small component cleanups/renames and prop/emit typings; minor README formatting fixes.

• CI/workflow and scripts polishing (lint/prettier run against repo root).

Relevant Technical Choices

• ESLint 9 flat config:

  • eslint.config.mjs uses vue-eslint-parser, eslint-plugin-vue flat preset, and @typescript-eslint for TS/.vue <script> blocks.
  • Scripts simplified to eslint . / eslint . --fix.

• Prettier:

  • .prettierrc.json with semi: false, singleQuote: true, printWidth: 100, vueIndentScriptAndStyle: true, etc.
  • Scripts expanded to run on the whole repo; ignores build artifacts/IDE dirs/lockfiles.

• Vitest coverage:

  • Swap @vitest/coverage-c8 → @vitest/coverage-v8 for Vitest 3 compatibility.

• Sass:

  • Replace chained @imports with an @forward barrel (src/styles/index.scss) to align with Dart Sass deprecation.

• Build outputs:

  • Keep vite-plugin-dts with rollupTypes: true; TypeScript 5.9 warning about API Extractor noted but non-blocking.

User-facing changes

• No breaking API changes to component props/emits intended.
• Styles should remain functionally equivalent; migration to Sass modules is internal.

Checklist

• Builds with Vite 7
• Tests pass with Vitest 3
• ESLint/Prettier run cleanly
• Sass deprecation warnings addressed

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