feat(api): M-04 添加版本信息端点

- 添加 /version 端点返回版本信息
- 版本变量支持构建时 ldflags 注入
- 返回 version、commit、build_time、go_version

internal/app/version_test.go

@@ -0,0 +1,73 @@
+package app
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"runtime"
+	"testing"
+)
+
+func TestHandleVersion(t *testing.T) {
+	req := httptest.NewRequest("GET", "/version", nil)
+	rr := httptest.NewRecorder()
+
+	handleVersion(rr, req)
+
+	if rr.Code != http.StatusOK {
+		t.Errorf("Expected status 200, got %d", rr.Code)
+	}
+
+	contentType := rr.Header().Get("Content-Type")
+	if contentType != "application/json" {
+		t.Errorf("Expected Content-Type application/json, got %s", contentType)
+	}
+
+	var info VersionInfo
+	if err := json.Unmarshal(rr.Body.Bytes(), &info); err != nil {
+		t.Fatalf("Failed to decode response: %v", err)
+	}
+
+	// 验证版本字段
+	if info.Version == "" {
+		t.Error("Version should not be empty")
+	}
+	if info.Version != version {
+		t.Errorf("Version = %q, want %q", info.Version, version)
+	}
+
+	// 验证 Go 版本
+	if info.GoVersion != runtime.Version() {
+		t.Errorf("GoVersion = %q, want %q", info.GoVersion, runtime.Version())
+	}
+
+	// Commit 和 BuildTime 可能为默认值
+	if info.Commit == "" {
+		t.Error("Commit should not be empty (may be 'unknown' during development)")
+	}
+	if info.BuildTime == "" {
+		t.Error("BuildTime should not be empty (may be 'unknown' during development)")
+	}
+}
+
+func TestVersionEndpoint_Integration(t *testing.T) {
+	handler := NewAPIHandler("", ActionSet{})
+
+	req := httptest.NewRequest("GET", "/version", nil)
+	rr := httptest.NewRecorder()
+
+	handler.ServeHTTP(rr, req)
+
+	if rr.Code != http.StatusOK {
+		t.Errorf("Expected status 200, got %d", rr.Code)
+	}
+
+	var info VersionInfo
+	if err := json.Unmarshal(rr.Body.Bytes(), &info); err != nil {
+		t.Fatalf("Failed to decode response: %v", err)
+	}
+
+	if info.Version != version {
+		t.Errorf("Version = %q, want %q", info.Version, version)
+	}
+}