Add on-site writeups with markdown support

[3rdit]

This PR adds inline write-up viewing and web-based markdown editor for submitting solutions on the website directly with a preview feature. I've added XOR encryption ("obfuscation") to prevent scraping that could cause problems with SEO.

The downloadable archive remains available as a fallback for every solution.

The main additions are a new solution view page at /solution/<hexid> that renders markdown content inline, and a web editor at /upload/solution/<hexid>/editor with live preview and character count validation. A new crypto service handles the obfuscation, and the reviewer approval flow now extracts markdown content from uploads and zips to create the obfuscated .bin files served to the users.

On the frontend, the solution pages use DOMPurify and marked.js for safe client-side markdown rendering, with copy buttons on code blocks. The crackme and user profile pages now link to the new view page instead of directly to the zip download.

This is quite a change so I will keep this draft to iron out any possible issues during further testing and post @xusheng6's review.

Closes #99

[xusheng6]

@3rdit what is the status on this? Is this ready for review?

[3rdit]

@xusheng6

I just did an additional code review and I believe it's all ready, I've rebased and prepared it so the merge conflicts are gone, should be good to go. Please let me know if there's anything else left, otherwise, it should work fine.