feat: add /admin/templates/preview endpoint; add preview button to template editor

templates/admin/templates.html

@@ -67,9 +67,14 @@
                         <label class="form-label">模板内容</label>
                         <textarea class="form-control" name="template_content" id="templateContent" rows="3" required placeholder="收到{trans_amt}元"></textarea>
                     </div>
+                    <div class="mb-3">
+                        <label class="form-label">示例 Payload (JSON, 可选，用于预览)</label>
+                        <textarea class="form-control font-monospace" id="templateSample" rows="4" placeholder='{"trans_amt": 100, "trans_order_info": {"remark": "abc"}}'></textarea>
+                    </div>
                 </div>
                 <div class="modal-footer">
                     <button type="button" class="btn btn-secondary" data-bs-dismiss="modal">取消</button>
+                    <button type="button" class="btn btn-outline-secondary" onclick="previewTemplate()">预览</button>
                     <button type="submit" class="btn btn-primary">保存</button>
                 </div>
             </div>
@@ -88,6 +93,7 @@
         document.getElementById('templateId').value = "";
         document.getElementById('templateName').value = "";
         document.getElementById('templateContent').value = "";
+        document.getElementById('templateSample').value = '';
         modal.show();
     }
 
@@ -97,7 +103,38 @@
         document.getElementById('templateId').value = id;
         document.getElementById('templateName').value = name;
         document.getElementById('templateContent').value = content;
+        document.getElementById('templateSample').value = '';
         modal.show();
     }
+
+    async function previewTemplate() {
+        const content = document.getElementById('templateContent').value;
+        let sample = {};
+        try {
+            const sampleText = document.getElementById('templateSample').value;
+            if (sampleText && sampleText.trim()) {
+                sample = JSON.parse(sampleText);
+            }
+        } catch (e) {
+            alert('示例 payload JSON 格式错误: ' + e);
+            return;
+        }
+
+        try {
+            const res = await fetch('/admin/templates/preview', {
+                method: 'POST',
+                headers: { 'Content-Type': 'application/json' },
+                body: JSON.stringify({ template_content: content, sample_payload: sample })
+            });
+            const data = await res.json();
+            if (res.ok) {
+                alert('渲染结果:\\n' + data.rendered);
+            } else {
+                alert('预览失败: ' + (data.error || '未知错误'));
+            }
+        } catch (e) {
+            alert('请求错误: ' + e);
+        }
+    }
 </script>
 {% endblock %}