feat(knowledge): breadcrumb分块上下文 & LookupKnowledgeTool日志优化

- DocumentChunk新增breadcrumb字段，分块时构建完整标题层级路径
- DocumentChunkService splitByHeadings维护标题层级栈算法
- VectorIndexService 将breadcrumb写入Milvus metadata
- LookupKnowledgeTool日志替换为结构化摘要，替代原始MD预览
- L0返回策略：唯一匹配用正文摘要，多匹配+L1有结果仅元数据（不读文件）
- 新增buildCompactSummary / buildMetadataOnlySummary方法
- 安装frontend-design skill
- 创建mvp/文档目录（架构设计+会话存储方案）
- 更新测试适配新逻辑

src/main/java/com/superbiz/agent/service/DocumentChunkService.java

@@ -56,7 +56,7 @@ public class DocumentChunkService {
     }
 
     /**
-     * 按照 Markdown 标题分割文档
+     * 按照 Markdown 标题分割文档，同时构建面包屑层级路径
      */
     private List<Section> splitByHeadings(String content) {
         List<Section> sections = new ArrayList<>();
@@ -65,20 +65,34 @@ public class DocumentChunkService {
         Pattern headingPattern = Pattern.compile("^(#{1,6})\\s+(.+)$", Pattern.MULTILINE);
         Matcher matcher = headingPattern.matcher(content);
 
+        // 标题层级栈：维护当前标题的完整路径
+        List<String> headingStack = new ArrayList<>();
         int lastEnd = 0;
-        String currentTitle = null;
+        String currentBreadcrumb = null;
 
         while (matcher.find()) {
+            int level = matcher.group(1).length(); // #→1, ##→2, ###→3 ...
+            String title = matcher.group(2).trim();
+
             // 保存上一个章节
             if (lastEnd < matcher.start()) {
                 String sectionContent = content.substring(lastEnd, matcher.start()).trim();
                 if (!sectionContent.isEmpty()) {
-                    sections.add(new Section(currentTitle, sectionContent, lastEnd));
+                    sections.add(new Section(
+                        headingStack.isEmpty() ? null : headingStack.get(headingStack.size() - 1),
+                        level,
+                        currentBreadcrumb,
+                        sectionContent,
+                        lastEnd));
                 }
             }
 
-            // 更新当前标题
-            currentTitle = matcher.group(2).trim();
+            // 维护层级栈：同级别或更高级别 → 弹出，低级 → 追加
+            while (!headingStack.isEmpty() && headingStack.size() >= level) {
+                headingStack.remove(headingStack.size() - 1);
+            }
+            headingStack.add(title);
+            currentBreadcrumb = String.join(" > ", headingStack);
             lastEnd = matcher.start();
         }
 
@@ -86,13 +100,18 @@ public class DocumentChunkService {
         if (lastEnd < content.length()) {
             String sectionContent = content.substring(lastEnd).trim();
             if (!sectionContent.isEmpty()) {
-                sections.add(new Section(currentTitle, sectionContent, lastEnd));
+                sections.add(new Section(
+                    headingStack.isEmpty() ? null : headingStack.get(headingStack.size() - 1),
+                    headingStack.size(),
+                    currentBreadcrumb,
+                    sectionContent,
+                    lastEnd));
             }
         }
 
         // 如果没有找到任何标题，将整个文档作为一个章节
         if (sections.isEmpty()) {
-            sections.add(new Section(null, content, 0));
+            sections.add(new Section(null, 0, null, content, 0));
         }
 
         return sections;
@@ -111,6 +130,7 @@ public class DocumentChunkService {
         List<DocumentChunk> chunks = new ArrayList<>();
         String content = section.content;
         String title = section.title;
+        String breadcrumb = section.breadcrumb;
 
         // 短章节直接作为一个分片（用 token 估算替代字符数做短路判断）
         if (content.length() <= chunkConfig.getMaxSize()
@@ -121,6 +141,7 @@ public class DocumentChunkService {
                 .endOffset(section.startIndex + content.length())
                 .chunkIndex(startChunkIndex)
                 .title(title)
+                .breadcrumb(breadcrumb)
                 .build();
             chunks.add(chunk);
             return chunks;
@@ -155,7 +176,7 @@ public class DocumentChunkService {
                         logger.debug("  触及硬上限 ({} tokens)，强制切分", tokenCount + paraTokens);
                         chunkParaStart = saveChunkAndGetNextStart(
                             chunks, section, paraPositions,
-                            chunkParaStart, i, title, chunkIndex);
+                            chunkParaStart, i, title, breadcrumb, chunkIndex);
                         chunkIndex++;
 
                         String prevChunkContent = chunks.get(chunks.size() - 1).getContent();
@@ -168,7 +189,7 @@ public class DocumentChunkService {
                     // 安全切点：段落边界
                     chunkParaStart = saveChunkAndGetNextStart(
                         chunks, section, paraPositions,
-                        chunkParaStart, i, title, chunkIndex);
+                        chunkParaStart, i, title, breadcrumb, chunkIndex);
                     chunkIndex++;
 
                     // 新分片以重叠文本开头
@@ -194,6 +215,7 @@ public class DocumentChunkService {
                 .endOffset(section.startIndex + actualEnd)
                 .chunkIndex(chunkIndex)
                 .title(title)
+                .breadcrumb(breadcrumb)
                 .build();
             chunks.add(chunk);
         }
@@ -213,6 +235,7 @@ public class DocumentChunkService {
             int fromPara,
             int toPara,
             String title,
+            String breadcrumb,
             int chunkIndex) {
 
         int actualStart = paraPositions.get(fromPara).start;
@@ -225,6 +248,7 @@ public class DocumentChunkService {
             .endOffset(section.startIndex + actualEnd)
             .chunkIndex(chunkIndex)
             .title(title)
+            .breadcrumb(breadcrumb)
             .build();
         chunks.add(chunk);
 
@@ -392,12 +416,16 @@ public class DocumentChunkService {
      * 章节数据类
      */
     private static class Section {
-        String title;
-        String content;
-        int startIndex;
+        String title;        // 最近一级标题名称
+        int level;           // 标题级别（1-6），0=无标题
+        String breadcrumb;   // 完整面包屑路径
+        String content;      // 章节内容
+        int startIndex;      // 在原文中的起始偏移
 
-        Section(String title, String content, int startIndex) {
+        Section(String title, int level, String breadcrumb, String content, int startIndex) {
             this.title = title;
+            this.level = level;
+            this.breadcrumb = breadcrumb;
             this.content = content;
             this.startIndex = startIndex;
         }