feat: Added SKILL.md for Flet Framework

[gopalparashar421]

Description

Added a SKILL.md in .github folder for public users to assist with Agentic Coding. It follows the SKILL.md specifications and hence can be easily used with any other IDE of your choice.

Type of change

• New feature (non-breaking change which adds functionality)

Checklist

• I signed the CLA.
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• New and existing tests pass locally with my changes
• I have made corresponding changes to the documentation (if applicable)

Additional details

The skill is currently available in .github folder since I work with Copilot but it can be easily used with any other IDE of your choice.

Summary by Sourcery

Documentation:

• Introduce a comprehensive SKILL.md guide for Flet covering setup, controls, layout, navigation, theming, state management, async patterns, extensions, packaging, and CLI usage.

[sourcery-ai]

We've reviewed this pull request using the Sourcery rules engine

[FeodorFitsner]

I like the beginning, was thinking about something like that. However, I think controls reference starting from line 812 is more the function of MCP, isn't it? I mean it probably works now, but who is going to keep that reference up-to-date and how, right?