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>

plugins/meigen-ai-design/.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "meigen-ai-design",
-  "version": "1.2.3",
-  "description": "Turn Claude Code into a visual creative assistant rivaling Lovart — AI image generation with creative workflow orchestration, parallel multi-direction output, prompt engineering skills, and a 1,300+ curated inspiration library. Supports local ComfyUI, MeiGen Cloud, and OpenAI APIs.",
+  "version": "1.0.0",
+  "description": "AI image generation with creative workflow orchestration, parallel multi-direction output, prompt engineering, and a 1,300+ curated inspiration library. Requires MeiGen MCP server (supports MeiGen Cloud, local ComfyUI, and OpenAI-compatible APIs).",
   "author": {
     "name": "MeiGen",
     "url": "https://www.meigen.ai"