refactor: 重构Neovim配置结构并更新文档

- 调整配置文件组织方式，新增init.lua作为入口
- 更新lazy-lock.json同步插件版本
- 完善lua/目录下的插件和配置模块结构
- 修改README.md补充配置说明和使用指南

lua/plugins/gitsigns.lua

@@ -0,0 +1,15 @@
+return {
+	"lewis6991/gitsigns.nvim",
+	config = function()
+		require("gitsigns").setup({
+			signs = {
+				add = { text = "+" },
+				change = { text = "~" },
+				delete = { text = "_" },
+				topdelete = { text = "‾" },
+				changedelete = { text = "~" },
+			},
+			current_line_blame = true,
+		})
+	end,
+}