feat(skills): Generate C4 diagrams using Mermaid

### Skill Name

c4-mermaid

### Programming Language

PowerShell

### Purpose

This skill can be used to generate C4 diagrams using Mermaid syntax.
C4 diagrams can be used to design and document the architecture of software systems using the 4 well-established C4 abstraction levels.

### Prerequisites

Self-validation might require [mermaid-cli](https://github.com/mermaid-js/mermaid-cli)

### Requirements

1. Generates consistent architecture diagrams for all 4 abstraction levels:
- system
- container
- component
- code

2. Embeds the diagrams in .md or dedicated .mmd files