feat(cli): 新增 AI 智能 Commit Message 生成与多语言支持

- 新增 `git air msg` 命令，支持根据暂存区或历史 Diff 自动生成 Conventional Commits 提交说明
- 支持中、英、日、韩多语言自适应及通过 CLI/配置文件/环境变量进行定制
- 完善全局配置体系，新增 `commit_lang` 选项及相关单元测试

internal/reviewer/msg_test.go

@@ -0,0 +1,58 @@
+package reviewer
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestDetectLanguage(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected string
+	}{
+		{"zh", "zh"},
+		{"ZH", "zh"},
+		{"zh-CN", "zh"},
+		{"中文", "zh"},
+		{"ja", "ja"},
+		{"ja-JP", "ja"},
+		{"Japanese", "ja"},
+		{"日本語", "ja"},
+		{"ko", "ko"},
+		{"ko-KR", "ko"},
+		{"한국어", "ko"},
+		{"en", "en"},
+		{"en-US", "en"},
+		{"English", "en"},
+		{"fr", "en"}, // 未预置语言回退到 en
+	}
+
+	for _, tt := range tests {
+		got := DetectLanguage(tt.input)
+		if got != tt.expected {
+			t.Errorf("DetectLanguage(%q) = %q, expected %q", tt.input, got, tt.expected)
+		}
+	}
+}
+
+func TestBuildCommitMsgPrompt(t *testing.T) {
+	langs := []struct {
+		lang     string
+		expected string
+	}{
+		{"zh", "简体中文"},
+		{"ja", "日本語"},
+		{"ko", "한국어"},
+		{"en", "English"},
+	}
+
+	for _, tt := range langs {
+		prompt := BuildCommitMsgPrompt(tt.lang)
+		if !strings.Contains(prompt, tt.expected) {
+			t.Errorf("BuildCommitMsgPrompt(%q) 应包含语言名称 %q", tt.lang, tt.expected)
+		}
+		if !strings.Contains(prompt, "Conventional Commits") {
+			t.Errorf("BuildCommitMsgPrompt(%q) 应包含 Conventional Commits 说明", tt.lang)
+		}
+	}
+}