feat(traffic): 正文入库 + 全文搜索，删除改为 SQL 事务

流量录制不再镜像 URL 路径写文件树，改为整条 exchange 落 SQLite：

- record: 元数据/头/正文写库；>256KB 的 body 才溢出到 _blobs（单层
  桶、按 hash 去重），库里留 8KB 预览 + 指针。文本正文全量喂 trigram
  FTS 索引（二进制按 content-type 跳过），支持任意子串与中文全文搜索。
- 删除退化为一个 SQL 事务级联删四张表，host 树后台异步回收，不再在
  写锁内 RemoveAll + 全树扫描——删除从数小时降到毫秒级，期间不再停摆录制。
- gcBlobs 改走 blob_refs 反查，顺带清理空桶目录；保留对旧文件树的
  引用扫描与 Get 回落，历史数据免迁移仍可读、可搜(元数据)、可删。
- 新增 traffic_blob 工具与 GET /api/traffic/blob 流式下载大 body；
  traffic_search 增加 body_contains 全文参数。

新表均为 CREATE TABLE IF NOT EXISTS，旧库自动补建，无需 ALTER 迁移。

Claude-Session: https://claude.ai/code/session_01RtPQYJ8W1mcaace3sHWGDm

server/server.go

@@ -717,6 +717,7 @@ func (s *Server) Handler() http.Handler {
 	mux.HandleFunc("DELETE /api/traffic", s.deleteTraffic)
 	mux.HandleFunc("DELETE /api/traffic/hosts", s.deleteTrafficHosts)
 	mux.HandleFunc("GET /api/traffic/exchange", s.getTrafficExchange)
+	mux.HandleFunc("GET /api/traffic/blob", s.getTrafficBlob)
 	mux.HandleFunc("GET /api/commands", s.pgListCommands)
 	mux.HandleFunc("GET /api/llm/records", s.pgListLLMRecords)
 	mux.HandleFunc("DELETE /api/llm/records", s.pgDeleteLLMRecords)
@@ -2934,6 +2935,35 @@ func (s *Server) getTrafficExchange(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, 200, map[string]any{"req": req, "resp": resp})
 }
 
+// getTrafficBlob streams one oversized body by its sha256. Bodies past the inline
+// threshold are not carried by the exchange endpoint — it returns a preview plus
+// an "@blob sha256:<hash>" pointer — so this is how the UI fetches them whole.
+// Streamed rather than buffered: these are the bodies too large to hold in memory.
+func (s *Server) getTrafficBlob(w http.ResponseWriter, r *http.Request) {
+	tr := s.m.Traffic()
+	if tr == nil {
+		writeErr(w, 404, "traffic disabled")
+		return
+	}
+	hash := strings.TrimSpace(r.URL.Query().Get("hash"))
+	if hash == "" {
+		writeErr(w, 400, "missing hash")
+		return
+	}
+	f, size, err := tr.Blob(hash)
+	if err != nil {
+		writeErr(w, 404, err.Error())
+		return
+	}
+	defer f.Close()
+	w.Header().Set("Content-Type", "application/octet-stream")
+	w.Header().Set("Content-Length", strconv.FormatInt(size, 10))
+	w.Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=%q", hash+".bin"))
+	if _, err := io.Copy(w, f); err != nil {
+		log.Printf("[traffic] 下载 blob %s 中断：%v", hash, err)
+	}
+}
+
 // getSettings returns the runtime app settings the UI toggles. The Brave API key
 // is returned as a boolean presence flag (brave_key_set), never the value itself,
 // so the UI can show "configured" without echoing the secret back.