Address review feedback: restructure plugin for marketplace conventions

- Remove .mcp.json (not used in marketplace, add README instead)
- Add marketplace.json entry for plugin discovery
- Add README.md with MCP server setup guide, provider config, and troubleshooting
- Add tools: declaration to image-generator agent (functional fix)
- Move <example> blocks from YAML frontmatter to markdown body
- Remove unused tools: Read, Grep, Glob from prompt-crafter agent
- Remove redundant name: field from command frontmatter
- Use full MCP tool prefix (mcp__meigen__*) in commands
- Rewrite plugin.json description to factual style
- Pin npm version to meigen@1.2.5

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.claude-plugin/marketplace.json

@@ -945,6 +945,19 @@
       "homepage": "https://github.com/wshobson/agents",
       "license": "MIT",
       "category": "languages"
+    },
+    {
+      "name": "meigen-ai-design",
+      "source": "./plugins/meigen-ai-design",
+      "description": "AI image generation with creative workflow orchestration, prompt engineering, and curated inspiration library via MCP server",
+      "version": "1.0.0",
+      "author": {
+        "name": "MeiGen",
+        "url": "https://github.com/jau123"
+      },
+      "homepage": "https://github.com/jau123/MeiGen-AI-Design-MCP",
+      "license": "MIT",
+      "category": "creative"
     }
   ]
 }