Add Hybrid Cryptosystem article

[xrissoula]

Description

This PR adds documentation for Polykey’s Hybrid Cryptosystem, which combines symmetric and asymmetric encryption. The document covers:

• The key encapsulation mechanism (KEM) for encrypting symmetric keys
• The data encapsulation scheme (DES) for encrypting bulk data
• Why hybrid encryption is more efficient than pure asymmetric encryption

This document ensures that users understand how Polykey secures data at rest and in transit using a hybrid approach.

Issues Fixed

• Relates Create Article in Polykey-Docs Explaining the Polykey Elliptic Curve Article #119
• Clarifies how Polykey encrypts large data efficiently
• Documents Polykey’s KEM and DES approach

Tasks

• 1. Added hybrid-cryptosystem.md to docs/reference/
• 2. Checked structure for readability and completeness
• 3. Verified cryptographic details with existing standards

Final checklist

• Domain specific tests
• Full tests
• Updated inline-comment documentation
• Lint fixed
• Squash and rebased
• Sanity check the final build

[xrissoula]

This PR is closed in favor of #135