feat: 新增 jsc-eli5 外掛，以大圖少字的 HTML 圖解簡單解釋主題

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

plugins/jsc-eli5/.claude-plugin/plugin.json

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+{
+  "name": "jsc-eli5",
+  "version": "0.0.1",
+  "description": "用最簡單的方式解釋任何主題：大圖少字的 HTML 圖解。使用 /jsc-eli5:eli5 <主題>",
+  "license": "MIT",
+  "skills": "./skills",
+  "author": {
+    "name": "JSC"
+  },
+  "keywords": ["explain", "eli5", "learning", "explainer", "html"]
+}

plugins/jsc-eli5/skills/eli5/SKILL.md

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+---
+name: eli5
+description: Explain a topic like I'm a 5 year old. Use when the user types /eli5 <topic> or asks for a dead-simple picture explainer of how something works.
+---
+
+# eli5
+
+Explain like I'm someone who knows nothing about this topic, using a HTML artifact with big pictures and few words.
+
+Topic: $ARGUMENTS