feat(cli): 优化 log 子命令并引入 LogLevel 强类型解析,重构 commands.lua 注册表解析与校验逻辑

- 调整 LogLevel 的 FromStr 错误类型为 String，适配 clap 的 value_parser
- log 子命令直接绑定 LogLevel 枚举，消除硬编码校验与类型转换
- 规范化日志级别更新与配置读取逻辑
- handler 类型有 Function 改为 String

commands/commands.lua

@@ -0,0 +1,37 @@
+-- commands/commands.lua
+function command(mod_path)
+    -- 无论输入 "a/b/c" 还是 "a\b\c"，统一替换为标准的 "a.b.c"
+    local normalized = mod_path:gsub("[/\\]", ".")
+
+    return {
+        __is_lazy_command = true,
+        module = normalized
+    }
+end
+
+
+return {
+    -- 1. 单文件子命令 (commands/use.lua)
+    ["use"] = {
+        description = "Switch the active version of a tool",
+        handler = command("use")
+    },
+
+    -- 2. 单文件子命令 (commands/list.lua)
+    ["list"] = {
+        description = "List available and currently activated versions",
+        handler = command("list")
+    },
+
+    -- 3. 复杂多文件子命令 (加载 commands/log/init.lua)
+    ["log"] = {
+        description = "View or configure mirror runtime logs",
+        handler = command("log")
+    },
+
+    -- 4. 支持别名快捷映射 (例如 mr ls 等价于 mr list)
+    ["ls"] = {
+        description = "Alias for list",
+        handler = command("list")
+    }
+}