docs: add workspace example + README workspace section

- examples/04-workspace/: 3-member workspace (core + greeter + hello)
- README.md: add workspace section with usage overview

Author: Sunrisepeak

README.md

@@ -65,6 +65,29 @@ mcpp run
 
 注: 初次构建需要初始化环境并获取工具链, 可能需要一些时间
 
+## 工作空间 (Workspace)
+
+mcpp 支持多包工作空间，在一个仓库中管理多个相关的库和应用：
+
+```toml
+# 根 mcpp.toml
+[workspace]
+members = ["libs/core", "libs/http", "apps/server"]
+
+[workspace.dependencies.compat]
+mbedtls = "3.6.1"
+```
+
+```bash
+mcpp build              # 构建所有 member
+mcpp build -p server    # 只构建 server 及其依赖
+```
+
+- member 之间用 `path = "..."` 声明依赖
+- `.workspace = true` 继承 workspace 统一管理的依赖版本
+- 工具链配置可继承和覆盖
+- 详见 [examples/04-workspace](examples/04-workspace/)
+
 ## 文档
 
 - [快速开始](docs/00-getting-started.md)

examples/04-workspace/README.md

@@ -0,0 +1,33 @@
+# 04 — workspace
+
+多包工作空间示例：两个库 + 一个应用，共享 namespace。
+
+```
+04-workspace/
+├── mcpp.toml              # [workspace] 声明 members
+├── libs/
+│   ├── core/              # 基础库 → export module demo.core
+│   └── greeter/           # 依赖 core → export module demo.greeter
+└── apps/
+    └── hello/             # 依赖 greeter → 可执行文件
+```
+
+## 构建 & 运行
+
+```bash
+cd 04-workspace
+
+# 从 workspace 根目录构建（自动选择 hello 作为构建目标）
+mcpp build
+mcpp run
+
+# 指定构建某个 member
+mcpp build -p hello
+```
+
+## 要点
+
+- 根 `mcpp.toml` 只有 `[workspace]`，没有 `[package]`（虚拟工作空间）
+- member 之间用 `path = "..."` 声明依赖，与普通项目完全一致
+- 所有 member 共享同一个 namespace（`demo`），module 名为 `demo.core`、`demo.greeter`
+- C++ module 的 `export` / `import` 控制接口可见性，构建工具不做额外限制

examples/04-workspace/apps/hello/mcpp.toml

@@ -0,0 +1,7 @@
+[package]
+namespace = "demo"
+name      = "hello"
+version   = "0.1.0"
+
+[dependencies]
+greeter = { path = "../../libs/greeter" }

examples/04-workspace/apps/hello/src/main.cpp

@@ -0,0 +1,9 @@
+import std;
+import demo.greeter;
+import demo.core;
+
+int main() {
+    std::println("{}", demo::greeter::greet());
+    std::println("core version: {}", demo::core::version());
+    return 0;
+}

examples/04-workspace/libs/core/mcpp.toml

@@ -0,0 +1,7 @@
+[package]
+namespace = "demo"
+name      = "core"
+version   = "0.1.0"
+
+[targets.core]
+kind = "lib"

examples/04-workspace/libs/core/src/core.cppm

@@ -0,0 +1,10 @@
+export module demo.core;
+import std;
+
+export namespace demo::core {
+
+inline std::string version() { return "0.1.0"; }
+
+inline std::string greet_target() { return "World"; }
+
+}

examples/04-workspace/libs/greeter/mcpp.toml

@@ -0,0 +1,10 @@
+[package]
+namespace = "demo"
+name      = "greeter"
+version   = "0.1.0"
+
+[targets.greeter]
+kind = "lib"
+
+[dependencies]
+core = { path = "../core" }

examples/04-workspace/libs/greeter/src/greeter.cppm

@@ -0,0 +1,11 @@
+export module demo.greeter;
+import std;
+import demo.core;
+
+export namespace demo::greeter {
+
+inline std::string greet() {
+    return "Hello, " + demo::core::greet_target() + "!";
+}
+
+}

examples/04-workspace/mcpp.toml

@@ -0,0 +1,6 @@
+[workspace]
+members = [
+    "libs/core",
+    "libs/greeter",
+    "apps/hello",
+]