fix(data): merge 651 confirmed monitor near-duplicate records

Collapse identical re-imports from the amazon-monitor Kaggle dataset where the same physical monitor was ingested many times under different amazonmon-<row> slugs with byte-identical specs. For each (base_model_slug + full spec fingerprint) cluster, keep the lowest source_row as canonical, union source_urls, and delete the redundant files. Also merge one cross-source duplicate (asus-va24ehe rows 60 & 404: same VA24EHE, two title strings) keeping the cleaner title and adopting the more complete adaptive_sync=FreeSync attribute. 882 -> 231 monitor records. Genuine SKU/config variants left unmerged. Refs #296

Author: Seungpyo1007