Add artifact plugin

Adds a skill for creating interactive HTML artifacts — self-contained
single-file explorers with visual controls, live preview, and prompt
output with copy button.

Includes templates for:
- Design playgrounds (components, layouts, spacing, color, typography)
- Data explorers (SQL, APIs, pipelines, regex)
- Concept maps (learning, exploration, relationships)
- Writing tools (tone, structure, audience)

plugins/artifact/README.md

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+# Artifact Plugin
+
+Creates interactive HTML artifacts — self-contained single-file explorers that let users configure something visually through controls, see a live preview, and copy out a prompt.
+
+## What is an Artifact?
+
+An artifact is a self-contained HTML file with:
+- Interactive controls on one side
+- A live preview on the other
+- A prompt output at the bottom with a copy button
+
+The user adjusts controls, explores visually, then copies the generated prompt back into Claude.
+
+## When to Use
+
+Use this plugin when the user asks for an interactive artifact, playground, explorer, or visual tool for a topic — especially when the input space is large, visual, or structural and hard to express as plain text.
+
+## Templates
+
+The skill includes templates for common artifact types:
+- **design-playground** — Visual design decisions (components, layouts, spacing, color, typography)
+- **data-explorer** — Data and query building (SQL, APIs, pipelines, regex)
+- **concept-map** — Learning and exploration (concept maps, knowledge gaps, scope mapping)
+- **writing-tool** — Writing and content (tone, document structure, audience)
+
+## Installation
+
+Add this plugin to your Claude Code configuration to enable the artifact skill.