[Feature] Add a Skill for agents

**Is your feature request related to a problem? Please describe.**
Enable Agents to use the best chart for data visualization

**Describe the solution you'd like**
Ask claude to create a skill for agents based on the demo projects and the source code and the pics in the readme, so agents can quickly decide the capabilities of microchart: what type of charts it supports, how series are displayed on a chart, how small and large labels can be displayed, how to customize each chart, ...

**Describe alternatives you've considered**
Ask claude without skill. Not a great result. Uses many tokens for the same thing each time.

**Additional context**
agentic dev is already here

Review the demo projects, source code, and images in the README to identify Microcharts' supported chart types, series behavior, label handling, and customization options. The work is done when an agent skill captures these capabilities clearly enough for agents to choose and configure an appropriate chart without repeatedly researching the project.

Written by the indexing model from the issue text.