refactor: 提取 core 库 + 新增 CLI 版本

- 创建 Cargo workspace（core / src-tauri / cli 三 crate）
- core: 纯 Rust 库，零 Tauri 依赖，包含所有业务逻辑
- src-tauri/commands: 改为薄包装，调用 core 函数
- cli: 基于 clap 的命令行工具，支持 JSON 输出
- CLI 命令: list, add, remove, conflicts, scan, profile, check-admin

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

core/src/backup.rs

@@ -0,0 +1,68 @@
+use chrono::Local;
+use std::path::PathBuf;
+use winreg::enums::*;
+use crate::registry::{self, SYS_REG_PATH, USER_REG_PATH};
+
+fn backup_base_dir() -> PathBuf {
+    dirs::data_dir()
+        .or_else(dirs::home_dir)
+        .unwrap_or_else(|| PathBuf::from("."))
+        .join("PathEditor")
+        .join("backups")
+}
+
+/// 获取 APPDATA 路径下的备份目录
+
+pub fn get_appdata_dir() -> String {
+    backup_base_dir().to_string_lossy().to_string()
+}
+
+/// 备份当前注册表中的系统 PATH 和用户 PATH
+/// 在保存前调用，备份的是注册表中的当前值（保存前的状态）
+
+pub fn backup_registry(custom_dir: Option<String>) -> Result<String, String> {
+    let backup_dir = match custom_dir {
+        Some(ref dir) if !dir.is_empty() => std::path::PathBuf::from(dir),
+        _ => backup_base_dir(),
+    };
+
+    std::fs::create_dir_all(&backup_dir)
+        .map_err(|e| format!("无法创建备份目录: {}", e))?;
+
+    // 读取当前注册表中的值（保存前的旧值）
+    let sys_paths = registry::load_paths(
+        HKEY_LOCAL_MACHINE,
+        SYS_REG_PATH,
+        "系统",
+    )?;
+    let user_paths = registry::load_paths(
+        HKEY_CURRENT_USER,
+        USER_REG_PATH,
+        "用户",
+    )?;
+
+    let timestamp = Local::now().format("%Y%m%d_%H%M%S_%3f");
+    let filename = format!("path_backup_{}.txt", timestamp);
+    let filepath = backup_dir.join(&filename);
+
+    let mut content = String::new();
+    content.push_str(&format!(
+        "PathEditor Backup - {}\n",
+        Local::now().format("%Y-%m-%d %H:%M:%S")
+    ));
+    content.push_str("\n[System PATH]\n");
+    for path in &sys_paths {
+        content.push_str(&format!("{}\n", path));
+    }
+    content.push_str("\n[User PATH]\n");
+    for path in &user_paths {
+        content.push_str(&format!("{}\n", path));
+    }
+
+    std::fs::write(&filepath, &content)
+        .map_err(|e| format!("无法写入备份文件: {}", e))?;
+
+    let result = filepath.to_string_lossy().to_string();
+    log::info!("备份已保存到: {}", result);
+    Ok(result)
+}