[BUG] 115离线下载 相同链接汇重复添加，并占用配额

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OpenList Version (required)

v4.1.3

Storage Driver Used (required)

115

Bug Description (required)

BUG复现：添加115离线任务，同一链接，会重复任务，配额也会减一

Configuration File Content (required)

Logs (optional)

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Reproduction Link (optional)

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Start by reproducing the issue in OpenList v4.1.3 with the 115 storage driver, submitting the same offline-download URL twice. Trace the 115 offline-task handling and quota accounting, then verify that duplicate submissions no longer create another task or consume quota. The report provides configuration but no source file or test entry point.