[Feature] Enable E2EE Support

[MuNeNICK]

This feature adds end-to-end encryption (E2EE) support to RefMD, with the objective of ensuring that server administrators cannot view documents or attached files.

This enables the use of sensitive documents, such as those containing passwords.

[MuNeNICK]

The PoC implementation has been completed locally, and security improvements and code refactoring are currently in progress.

• Key management support
• Document encryption
• Use of Yjs with encrypted documents
• Migration of rendering from backend to frontend
• Migration of search to frontend
• Migration of Git functionality to frontend
• Migration of export functionality to frontend
• Encryption of attached files

WIP

• Migration of existing data
• Testing of existing systems
• Security assessment

[MuNeNICK]

Additionally, this work should make it easier to turn the product into a desktop application. We are considering implementing a desktop client using Tauri.