fix: 左右两栏实时渲染、修复 HTTP 环境复制按钮

- 生成过程中两栏布局始终可见，结构化字段实时更新
- 流式阶段显示在两栏上方，完成后仅隐藏流式指示器
- 复制功能增加 navigator.clipboard 存在性检查
- HTTP 环境降级为 textarea + execCommand fallback

templates/pages/generate.html

@@ -217,7 +217,6 @@
             btn.textContent = '生成中...';
             btn.classList.add('opacity-70', 'cursor-not-allowed');
             output.classList.remove('hidden');
-            outputContent.classList.add('hidden');
             streaming.classList.remove('hidden');
             document.getElementById('streaming-text').textContent = '';
             document.getElementById('streaming-status').textContent = '';
@@ -281,9 +280,8 @@
                     // Assemble full markdown from structured fields
                     markdownContent = buildMarkdown(fields);
                     document.getElementById('pr-markdown').textContent = markdownContent;
-                    // Switch from streaming to structured display
+                    // Hide streaming indicator; columns already visible
                     streaming.classList.add('hidden');
-                    outputContent.classList.remove('hidden');
                     btn.disabled = false;
                     btn.textContent = '生成 PR 描述';
                     btn.classList.remove('opacity-70', 'cursor-not-allowed');
@@ -291,7 +289,6 @@
                 error(data) {
                     showToast('生成失败: ' + (data.message || '未知错误'), 'error');
                     streaming.classList.add('hidden');
-                    output.classList.add('hidden');
                     btn.disabled = false;
                     btn.textContent = '生成 PR 描述';
                     btn.classList.remove('opacity-70', 'cursor-not-allowed');
@@ -320,24 +317,32 @@
                 showToast('没有可复制的内容，请先生成 PR 描述', 'warning');
                 return;
             }
+            // Clipboard API requires HTTPS; fallback to textarea for HTTP
+            if (navigator.clipboard && navigator.clipboard.writeText) {
                 navigator.clipboard.writeText(markdown).then(() => {
                     showToast('已复制到剪贴板', 'success');
                 }).catch(() => {
-                // Fallback for non-HTTPS or permission-denied contexts
+                    fallbackCopy(markdown);
+                });
+            } else {
+                fallbackCopy(markdown);
+            }
+        }
+
+        function fallbackCopy(text) {
             const textarea = document.createElement('textarea');
-                textarea.value = markdown;
-                textarea.style.position = 'fixed';
-                textarea.style.opacity = '0';
+            textarea.value = text;
+            textarea.style.cssText = 'position:fixed;left:0;top:0;opacity:0;';
             document.body.appendChild(textarea);
+            textarea.focus();
             textarea.select();
             try {
-                    document.execCommand('copy');
-                    showToast('已复制到剪贴板', 'success');
+                const ok = document.execCommand('copy');
+                showToast(ok ? '已复制到剪贴板' : '复制失败，请手动选择文本复制', ok ? 'success' : 'error');
             } catch (e) {
                 showToast('复制失败，请手动选择文本复制', 'error');
             }
             document.body.removeChild(textarea);
-            });
         }
 
         loadRefs();