feat: 拆分评审与提交消息提示词并增加 hook 备份与 JSON 输出

- 新增 custom_reviewer_prompt 和 custom_commit_msg_prompt，兼容旧 custom_prompt
- pre-commit hook 安装时备份已有 hook，卸载时恢复
- 支持 --format json 输出评审结果
- diff 发送前自动脱敏敏感信息

internal/reviewer/msg_test.go

@@ -56,3 +56,13 @@ func TestBuildCommitMsgPrompt(t *testing.T) {
 		}
 	}
 }
+
+func TestBuildCommitMsgPromptWithCustom(t *testing.T) {
+	prompt := BuildCommitMsgPromptWithCustom("en", "Use a short imperative subject and mention breaking changes explicitly.")
+	if !strings.Contains(prompt, "Use a short imperative subject") {
+		t.Fatal("自定义 Commit Message Prompt 未被合并")
+	}
+	if !strings.Contains(prompt, "Conventional Commits") {
+		t.Fatal("内置 Conventional Commits 约束不应丢失")
+	}
+}