feat: 统一 apps/mcp/services 为 entries/ Skill 格式

将 20 个条目从三个分散目录（apps/8、mcp/7、services/5）迁移到统一的
entries/ 目录。每个条目包含：
- manifest.json：极简结构化元数据
- install.md：自然语言安装说明（如适用）
- usage.md：自然语言使用说明和连接配置

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

entries/fetch-mcp/manifest.json

@@ -0,0 +1,19 @@
+{
+  "id": "fetch-mcp",
+  "name": "Fetch MCP",
+  "type": "mcp",
+  "version": "0.6.2",
+  "author": "Anthropic",
+  "description": "网页内容获取与转换，将网页转为 Markdown 供 LLM 使用",
+  "tags": [
+    "网页",
+    "抓取",
+    "Markdown"
+  ],
+  "icon": "terminal",
+  "platformSupport": [
+    "macos",
+    "windows",
+    "linux"
+  ]
+}