feat(mcp): inline presets in panel with one-click enable

- Show not-installed MCP presets directly in the list, consistent with existing UI (no modal)
- Toggle now supports enabling presets by writing to ~/.claude.json (mcpServers) and refreshing list
- Keep installed MCP entries unchanged (edit/delete/toggle)

fix(mcp): robust error handling and pre-submit validation

- Use extractErrorMessage in MCP panel and form to surface backend details
- Prevent pasting full config (with mcpServers) into single-server JSON field
- Add required-field checks: stdio requires non-empty command; http requires non-empty url

i18n: add messages for single-server validation and preset labels

chore: add data-only MCP presets file (no new dependencies)

src/config/mcpPresets.ts

@@ -0,0 +1,38 @@
+import { McpServer } from "../types";
+
+export type McpPreset = {
+  id: string;
+  name: string;
+  description: string;
+  tags?: string[];
+  server: McpServer;
+  homepage?: string;
+  docs?: string;
+  requiresEnv?: string[];
+};
+
+// 预设库（数据文件，当前未接入 UI，便于后续“一键启用”）
+export const mcpPresets: McpPreset[] = [
+  {
+    id: "github-issues",
+    name: "GitHub Issues",
+    description: "查询与管理 GitHub Issues（示例）",
+    tags: ["productivity", "dev"],
+    server: { type: "http", url: "https://mcp.example.com/github-issues" },
+    docs: "https://example.com/mcp/github-issues",
+    requiresEnv: ["GITHUB_TOKEN"],
+  },
+  {
+    id: "local-notes",
+    name: "本地笔记",
+    description: "访问本地笔记数据库（示例）",
+    tags: ["local"],
+    server: {
+      type: "stdio",
+      command: "/usr/local/bin/notes-mcp",
+      args: ["--db", "~/.notes/notes.db"],
+    },
+  },
+];
+
+export default mcpPresets;