前端新增 UsageLogExpandedDetail 点击展开面板和 BillingDetailSummary
hover 计费详情，后端修复 per_1m_tokens 任务结算日志的 completion_tokens
从零值改为写入 total_tokens 实际值。新增 taskBillingLogMerge 合并
任务预扣/结算日志。

Co-Authored-By: Claude <noreply@anthropic.com>

Replace bytes.Replace with gjson.GetBytes+sjson.SetBytes in passthrough
mode to correctly handle JSON whitespace variations and avoid silently
sending empty body on read errors. Also add log search count limit to
prevent slow COUNT queries on large log tables.