fix: 真正的流式输出 + 修复 Markdown 标题渲染

流式输出:
- 恢复 content 事件处理，实时累积 LLM 原始输出
- parsePartialJSON 从不完整 JSON 中渐进提取已闭合的字段
- 每次提取到新字段即更新两栏，实现左栏渐进渲染
- 结构化事件(title/detail等)覆盖解析结果，确保最终一致

Markdown 渲染:
- 重写为逐行处理(_renderLines)，不再按双换行分块
- ### 及更深层级标题在单换行后也能正确识别为独立块
- 列表项、水平线等同样受益于逐行解析

templates/pages/generate.html

@@ -184,48 +184,77 @@
             indicator.classList.remove('hidden');
 
             // Clear previous results
-            document.getElementById('pr-rendered').innerHTML = '';
+            document.getElementById('pr-rendered').innerHTML = '<span class="animate-pulse text-gray-400">正在生成...</span>';
             document.getElementById('pr-markdown').textContent = '';
             markdownContent = '';
 
-            // Helper: update both columns from current fields
             const fields = { title: '', type: '', summary: '', details: '', impact: '' };
+            let rawText = '';
+            let done = false;
+
             function updateColumns() {
                 markdownContent = buildMarkdown(fields);
                 document.getElementById('pr-rendered').innerHTML = renderMarkdown(markdownContent);
                 document.getElementById('pr-markdown').textContent = markdownContent;
             }
 
+            // Try to extract completed fields from partial JSON
+            function parsePartialJSON(text) {
+                const result = {};
+                for (const key of ['title', 'type', 'summary', 'details', 'impact']) {
+                    // Match "key": "value" where value's closing quote exists
+                    const re = new RegExp('"' + key + '"\\s*:\\s*"((?:[^"\\\\]|\\\\.)*)"');
+                    const m = text.match(re);
+                    if (m) result[key] = m[1].replace(/\\"/g, '"').replace(/\\n/g, '\n').replace(/\\\\/g, '\\');
+                }
+                return result;
+            }
+
             SSE.post(`/api/repos/${repoId}/generate`, {
                 base: baseRef,
                 head: headRef,
             }, {
+                content(data) {
+                    if (done) return;
+                    rawText += data.content || '';
+                    // Parse partial JSON to extract fields progressively
+                    const partial = parsePartialJSON(rawText);
+                    let changed = false;
+                    for (const key of ['title', 'type', 'summary', 'details', 'impact']) {
+                        if (partial[key] && partial[key] !== fields[key]) {
+                            fields[key] = partial[key];
+                            changed = true;
+                        }
+                    }
+                    if (changed) updateColumns();
+                },
                 title(data) {
-                    fields.title += data.content || '';
+                    fields.title = data.content || fields.title;
                     updateColumns();
                     document.getElementById('streaming-status').textContent = '解析标题...';
                 },
                 type(data) {
-                    fields.type += data.content || '';
+                    fields.type = data.content || fields.type;
                     updateColumns();
                     document.getElementById('streaming-status').textContent = '解析类型...';
                 },
                 summary(data) {
-                    fields.summary += data.content || '';
+                    fields.summary = data.content || fields.summary;
                     updateColumns();
                     document.getElementById('streaming-status').textContent = '解析摘要...';
                 },
                 detail(data) {
-                    fields.details += data.content || '';
+                    fields.details = data.content || fields.details;
                     updateColumns();
                     document.getElementById('streaming-status').textContent = '解析详细说明...';
                 },
                 impact(data) {
-                    fields.impact += data.content || '';
+                    fields.impact = data.content || fields.impact;
                     updateColumns();
                     document.getElementById('streaming-status').textContent = '解析影响范围...';
                 },
                 done() {
+                    done = true;
                     updateColumns();
                     indicator.classList.add('hidden');
                     btn.disabled = false;
@@ -233,6 +262,7 @@
                     btn.classList.remove('opacity-70', 'cursor-not-allowed');
                 },
                 error(data) {
+                    done = true;
                     showToast('生成失败: ' + (data.message || '未知错误'), 'error');
                     indicator.classList.add('hidden');
                     btn.disabled = false;