Clean Med_v1: drop 12 preface/foreword/index chunks missed by LLM judge

chunks/Med_v1/AnatomyAndPhysiology-LR.chunks.json

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chunks/Med_v1/Microbiology-LR.chunks.json

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chunks/Med_v1/Pharmacology-WEB.chunks.json

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chunks/Med_v1/Psychiatric-Mental_Health_Nursing-WEB.chunks.json

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chunks/Med_v1/biostat.chunks.json

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