refactor(mcp): switch to user-level config ~/.claude.json and remove project-level logic

- Read/write ~/.claude.json (preserve unknown fields) for mcpServers
- Remove settings.local.json and mcp.json handling
- Drop enableAllProjectMcpServers command and UI toggle
- Update types, Tauri APIs, and MCP panel to reflect new status fields
- Keep atomic write and command validation behaviors

src/vite-env.d.ts

@@ -64,7 +64,6 @@ declare global {
       // Claude MCP
       getClaudeMcpStatus: () => Promise<McpStatus>;
       readClaudeMcpConfig: () => Promise<string | null>;
-      setClaudeMcpEnableAllProjects: (enable: boolean) => Promise<boolean>;
       upsertClaudeMcpServer: (
         id: string,
         spec: Record<string, any>,