Refactor project structure into basic Python package layout

[BytecodeBrewer]

Goal

Organize the project into a clearer Python package structure.

Why

The project is growing from a calculator/API experiment into a small data application. A clean structure helps separate CLI, API access, conversion logic, GUI experiments and future analysis code.

Suggested structure

src/
  fx_converter_lab/
    __init__.py
    cli/
    clients/
    services/
    domain/
    config.py
tests/
temp/

Scope

Move reusable logic from scripts into package modules
Keep temp/ only for experiments and learning code
Separate API access, conversion logic and user interaction
Add minimal README note explaining the structure

Acceptance criteria

• Main reusable code lives under src/fx_converter_lab/
• Experimental code is clearly separated in temp/
• Imports work from the new structure
• README briefly explains the main folders
• Existing basic functionality still work

Note

Type: Chore / Refactor
Priority: Must
Area: Project Structure