Adds Skills Folder and Indicators Skill

[AlexCatarino]

Description

The Skills folder contains instruction sets that teach Claude how to perform complex, multi-file tasks following project-specific conventions such as create a new indicator, dataset, or brokerage integration.

In this PR, we add the first skill: Indicators.

Motivation and Context

Claude's skills will help contributors add new features to LEAN.

Requires Documentation Change

Mention Skills in the https://www.quantconnect.com/docs/v2/lean-engine/contributions/

How Has This Been Tested?

Used Indicator skills to generate SMA, CMO, and RSI indicators.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Refactor (non-breaking change which improves implementation)
• Performance (non-breaking change which improves performance. Please add associated performance test and results)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Non-functional change (xml comments/documentation/etc)

Checklist:

• My code follows the code style of this project.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• My branch follows the naming convention bug-<issue#>-<description> or feature-<issue#>-<description>