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-tauri/src/lib.rs

@@ -425,7 +425,6 @@ pub fn run() {
             // Claude MCP management
             commands::get_claude_mcp_status,
             commands::read_claude_mcp_config,
-            commands::set_claude_mcp_enable_all_projects,
             commands::upsert_claude_mcp_server,
             commands::delete_claude_mcp_server,
             commands::validate_mcp_command,