style(course/15): 优化代码格式与中文标点一致性

- 调整 hello_world.zig 代码注释与分号后空格，提升可读性
- 统一 README.md 分支命名说明中的中文标点用法
- 修正 build.zig 缩进，使结构更规范

Author: jinzhongjia

README.md

@@ -188,9 +188,9 @@ bun export-pdf   # 导出 PDF 版本
   - 使用中文标点符号
   - 代码块指定语言类型
 - **分支命名**:
-  - 功能: `feature/功能描述`
-  - 修复: `fix/问题描述`
-  - 文档: `docs/文档更新`
+  - 功能：`feature/功能描述`
+  - 修复：`fix/问题描述`
+  - 文档：`docs/文档更新`
 
 ### 内容编写指南
 

course/code/15/build_system/externalfile/build.zig

@@ -16,9 +16,9 @@ pub fn build(b: *std.Build) !void {
     const exe = b.addExecutable(.{
         .name = "zig",
         .root_module = b.addModule("zig", .{
-        .root_source_file = b.path("src/main.zig"),
-        .target = target,
-        .optimize = optimize,
+            .root_source_file = b.path("src/main.zig"),
+            .target = target,
+            .optimize = optimize,
         }),
     });
 

course/code/15/hello_world.zig

@@ -37,8 +37,8 @@ const Three = struct {
     // #region three
     pub fn main() !void {
         // 定义两个缓冲区
-        var stdout_buffer: [1024]u8 = undefined;// [!code focus]
-        var stderr_buffer: [1024]u8 = undefined;// [!code focus]
+        var stdout_buffer: [1024]u8 = undefined; // [!code focus]
+        var stderr_buffer: [1024]u8 = undefined; // [!code focus]
 
         // 获取writer句柄// [!code focus]
         var stdout_writer = std.fs.File.stdout().writer(&stdout_buffer);
@@ -49,8 +49,8 @@ const Three = struct {
         const stderr = &stderr_writer.interface;
 
         // 通过句柄写入buffer// [!code focus]
-        try stdout.print("Hello {s}!\n", .{"out"});// [!code focus]
-        try stderr.print("Hello {s}!\n", .{"err"});// [!code focus]
+        try stdout.print("Hello {s}!\n", .{"out"}); // [!code focus]
+        try stderr.print("Hello {s}!\n", .{"err"}); // [!code focus]
 
         try stdout.flush();
         try stderr.flush();
@@ -61,4 +61,3 @@ const Three = struct {
     }
     // #endregion three
 };
-