Description

Define all TypeScript interfaces for the application's data models.

Tasks

• Create interfaces for GistMetadata
• Create interfaces for UserMetadata
• Create interfaces for EncryptedData
• Create interfaces for API responses
• Create interfaces for error types
• Create type for binary file format
• Export all types from types/index.ts

Acceptance Criteria

• All types are properly documented with JSDoc comments
• Types follow the data models defined in docs/SPEC.md
• All types are exported from a central index file
• Types are edge-runtime compatible (no Node.js specific types)