nhtsa-edge-api: Offline NHTSA VIN Decoder

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A TypeScript port of NHTSA's spVinDecode that runs on Cloudflare Workers over the official monthly vPIC dump, so VIN decoding needs no call to NHTSA (p50 about 1.4 ms). Its output was compared with NHTSA's own SQL functions on 11,000 VINs with no unexplained differences, and it matches the live API on 95.4% of 1,000 VINs. The author also documents that spvindecode in the PostgreSQL dump never applies VinDescriptor overrides. Only vPIC is fully live; recalls and fuel economy are partial.