Private Repository

[hayesZach]

This PR adds the Private Repository implementation as well as the secret package used to generate API keys.

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Note

Implements a persistent private data layer and API key generation.

• New private repository using GORM with SQLite (private.db), auto-migrates Key, Marketplace, AdminAudit, enables FK + WAL, and seeds csfloat marketplace
• Bootstraps an admin API key per environment via a new secret key generator; logs the formatted one-time key and stores its SHA-256 hash as Key.ID
• Refactors models.Key to use string ID (hash), adds CreatedAt/UpdatedAt, and Environment; enforces env presence and admin scope constraints in BeforeCreate
• Updates RawKey to include string id and environment; adds Permissions.AddAllPermissions()
• Adjusts repository and service interfaces to use string IDs for keys; introduces domain/secret interfaces and concrete internal/secret implementation (env-based prefixes, random generation, hashed ID)
• Dependencies: adds gorm.io/driver/sqlite and related transitive deps

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[Step7750]

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