feat: Add Korean translation for assembly lessons

[notJoon]

WIP

Translating the assembly lessons into Korean, with plans to translate all available documents.

Note: Converted bold text separators to proper markdown headers for better rendering

[notJoon]

@kiwiyou @evenharder Thank you for the review. Translation is definitely difficult, but thanks to you, the sentences have become much more natural. I've tried to apply your suggestions as much as possible, so I'd be appreciate if you could take a look and confirm 👍