feat(s3): SwiftPM scaffold + DSKit data layer + 14-fixture acceptance
- Package.swift: AI (S2-owned) + DSKit (models/client/fixtures) + DSKitTests, tools 6.2, .swiftLanguageMode(.v6), .macOS(.v26)
- JSONValue (Sendable AnyCodable), DSDate (value-type ISO8601FormatStyle cascade, date-only UTC), explicit-CodingKeys decoder
- Models: Auth/Document(+Detail flat-compose, MD-first)/Catalog/Search+Ask/Memo/Digest; non-optional limited to id/file_type/created+updated_at/total
- DSClient protocol + FixtureDSClient (Bundle.module, zero backend) + DSError + DSConfig + DownloadURL (?token= query)
- Tests: 14-fixture contract acceptance (value asserts) + JSONValue number trap + Ask round-trip + AI router fallback/explicit-unavailable
swift build + swift test green (19 tests). Sources/AI untouched.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Hyungi
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