Implement first database/storage layer

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Goal

Implement the first database/storage layer for ARGUS based on the storage research.

Why

ARGUS needs persistent storage to move beyond temporary API requests and in-memory analytics. A first storage layer will make it possible to save historical data, reuse fetched data and prepare the project for stronger analytics and future reporting workflows.

This ticket should provide practical experience with SQL, schema design and database integration in a Python project.

Scope

• Add the selected database/storage dependency if needed
• Create a first minimal schema or storage structure
• Store historical market or exchange-rate data
• Add a small repository/storage module
• Add basic create/read workflow
• Keep storage logic separate from UI code
• Add tests for storage behavior where realistic
• Document setup and usage

Acceptance criteria

• Selected database/storage technology is added
• Minimal schema or storage structure exists
• Historical data can be saved
• Stored data can be read back for analytics
• Storage logic is separated from UI and API clients
• Basic tests or verification steps exist
• README or docs explain how to use the storage layer
• Existing tests still pass

Note

Priority: Should