add excalidraw-gen skill for structured diagram generation

[fizznix]

Pull Request Checklist

• I have read and followed the CONTRIBUTING.md guidelines.
• I have read and followed the Guidance for submissions involving paid services.
• My contribution adds a new instruction, prompt, agent, skill, or workflow file in the correct directory.
• The file follows the required naming convention.
• The content is clearly structured and follows the example format.
• I have tested my instructions, prompt, agent, skill, or workflow with GitHub Copilot.
• I have run npm start and verified that README.md is up to date.
• I am targeting the staged branch for this pull request.

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Description

Add excalidraw-gen skill for structured diagram generation

Overview

Introduces a new skill excalidraw-gen that generates Excalidraw diagram files from structured JSON/YAML input specifications. This provides a deterministic, CLI-driven approach to diagram creation with precise control over layout, styling, and rendering.

What's included

• SKILL.md — Overview and CLI reference
• schema.md — Complete input file schema (nodes, edges, top-level fields)
• node-types.md — All available node types for flowchart and architecture templates
• style-overrides.md — Per-node and per-edge styling options with color palette
• validation.md — Validation rules and error handling
• examples.md — Annotated JSON and YAML examples
• agent-workflow.md — Agent checklist and common diagram patterns

Key features

• Converts structured input → fully-laid-out .excalidraw files
• Supports flowchart and architecture templates
• Multiple layout options (dag, grid) and themes (default, pastel, dark)
• Designed for reproducible, automation-friendly diagram generation
• Complements excalidraw-diagram-generator (natural language approach)

CLI usage

npx excalidraw-gen generate <input.json|yaml> --template flowchart --theme default --out output.excalidraw
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## Type of Contribution

- [ ] New instruction file.
- [ ] New prompt file.
- [ ] New agent file.
- [ ] New plugin.
- [x] New skill file.
- [ ] New agentic workflow.
- [ ] Update to existing instruction, prompt, agent, plugin, skill, or workflow.
- [ ] Other (please specify):

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By submitting this pull request, I confirm that my contribution abides by the [Code of Conduct](../CODE_OF_CONDUCT.md) and will be licensed under the MIT License.

[github-actions]

🔍 Skill Validator Results

⚠️ Warnings or advisories found

Scope	Checked
Skills	1
Agents	1
Total	2
Severity	Count
---	---:
❌ Errors	0
⚠️ Warnings	1
ℹ️ Advisories	0

Summary

Level	Finding
ℹ️	Found 1 skill(s)
ℹ️	[excalidraw-gen] 📊 excalidraw-gen: 628 BPE tokens [chars/4: 740] (detailed ✓), 5 sections, 1 code blocks
ℹ️	[excalidraw-gen] ⚠ No numbered workflow steps — agents follow sequenced procedures more reliably.
ℹ️	✅ All checks passed (1 skill(s))

Full validator output

```text Found 1 skill(s) [excalidraw-gen] 📊 excalidraw-gen: 628 BPE tokens [chars/4: 740] (detailed ✓), 5 sections, 1 code blocks [excalidraw-gen] ⚠ No numbered workflow steps — agents follow sequenced procedures more reliably. ✅ All checks passed (1 skill(s)) ```

[fizznix]

@all-contributors add @fizznix for content, code

[allcontributors]

@fizznix

I've put up a pull request to add @fizznix! 🎉