Add support for multi-year tracking

[MozkaGit]

Description

Currently, the application only allows viewing and managing data for the current month. When attempting to add historical data (e.g., expenses from 2025), the data gets incorrectly associated with the current month instead of the original month/year.

Use Case

I want to import historical financial data CSV exports spanning 2025 to have a complete yearly overview and track my savings rate accurately over time.

[cachebag]

I want to import historical financial data CSV exports spanning 2025 to have a complete yearly overview and track my savings rate accurately over time.

Working on this now but we currently don't support CSV imports, only JSON (since that's the format we output data to).

CSV support is next though