Add KlingAiping usage-token settlement from upstream final_unit_deduction and duration fallback handling.

Normalize model endpoint config persistence and convert model pricing values between stored USD and display currency in the editor.

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

- 避免仅编辑展示价格时写入默认真实计费规则
- 将 video-extend 纳入 KlingAiping 原生渠道约束
- 补充相关保存决策、渠道约束和计费展示测试

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

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>