fix: Replace broken linting setup with ESLint 9 + Prettier for Svelte 5

Commit notes

- Remove old .eslintrc.cjs (ESLint 8 format conflicting with ESLint 9) - Rewrite eslint.config.js with proper flat config for ESLint 9 - Configure proper Svelte 5 support with eslint-plugin-svelte - Add VS Code/Cursor settings for format-on-save - Add recommended extensions for Svelte, Prettier, ESLint, Tailwind

The old setup had two conflicting ESLint configs (.eslintrc.cjs and eslint.config.js) which caused issues. This consolidates to ESLint 9's flat config format with proper TypeScript and Svelte 5 support.

Co-authored-by: armin.naimi <[email redacted]>