Add Prettier and ESLint configuration to projects

[Josephat-S]

This pull request adds Prettier and its Tailwind CSS plugin to all Next.js monolith templates (blog, ecommerce, portfolio, saas, school) to enforce consistent code formatting. It also updates ESLint configurations to integrate with Prettier and introduces new npm scripts for formatting and auto-fixing lint errors.

Formatting and linting improvements:

• Added .prettierrc configuration files with formatting rules and enabled the prettier-plugin-tailwindcss plugin for all templates.
• Updated .eslintrc.json files to extend from both next/core-web-vitals and prettier, ensuring ESLint and Prettier work together without conflicts.

Tooling and dependencies:

• Added prettier, prettier-plugin-tailwindcss, and eslint-config-prettier as dev dependencies in each template's package.json.
• Added new npm scripts: format (runs Prettier on the codebase) and lint:fix (runs ESLint with auto-fix), in addition to the existing lint script.

Closes #48