Added course purchases and auth system

[dhruvilmehta]

PR Fixes:

• 1 Added user registeration system
• 2 Purchase with Razorpay

Resolves #169

Checklist before requesting a review

• [X] I have performed a self-review of my code
• [] I assure there is no similar/duplicate pull request regarding same issue Similar to @devsargam but added a little tweaks to DB schema and URLs for buying courses.

UI is broken for now but can be done soon once this is approved.

Approach:

DB Schema

Flow of payment

Note: 8 files just have formatting changes due to prettier check while committing.

[fengstats]

@phy-lei 感谢建议~ 目前正在做这部分调整，现在项目中的 icon 全是使用 SVG 标签的方式引入，确实会影响开发时的代码阅读体验

不过迁移方案，暂时不考虑 UnoCSS 了，还是 Iconify for Tailwind CSS

也不用将所有 icon 管理都集成进来，需要什么 icon 自行安装对应的 icon 包即可，可以先找两个比较全面的包：https://icones.js.org/