Add Memex - Native desktop AI builder for Mac, Linux, and Windows

[chilang]

This PR adds Memex to the Coding Assistants section.

Memex is a desktop-native AI development environment that transforms natural language into working applications.

Key features:

• Desktop-native application for Mac, Linux, and Windows
• Converts natural language descriptions into working applications
• Local execution and iterative feedback
• Seamless integration with existing development workflow

The entry is added in alphabetical order under the Coding Assistants section.

Links:

• Website: https://memex.tech/