feat(magic): pairing-code login flow
Backend:
- MagicPairingCode + MagicSession Prisma models
- /api/magic/pair/create (6-digit code, 10min TTL, single-use)
- /api/magic/pair/redeem (no auth, returns mgc_* token)
- /api/magic/info (public DMG metadata)
- requireUser() accepts mgc_* tokens
Mac-App (RebreakMagic):
- LoginView: 6-digit code input (OTP-style), real AppIcon, no signup
- AuthService: signInWithPairingCode() replaces email/pw flow
Native-App:
- MagicSheet (TrueSheet) in Settings: download + code generator + linked Macs
- AddMacSheet: subtle banner pointing to /settings
- de/en locales
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