[codex] Use a named Python import package

[amarakramali]

What changed

• moved the runtime modules into the real src/aep_load_forecasting/ package layout
• updated internal imports, tests, console entry points, Streamlit integration, and documentation
• added a CI assertion that the wheel contains aep_load_forecasting and never exposes a top-level src package

Why

The v0.1.0 wheel treated the source container itself as the import package. A generic top-level src package is collision-prone and is not the standard PyPA src layout. The stable aep-* console commands remain unchanged; direct Python imports now use aep_load_forecasting.*.

Validation

• python -m pytest -q — 66 passed
• python -m ruff check src tests streamlit_app.py
• python -m compileall -q src tests streamlit_app.py
• python -m build
• verified wheel contents include aep_load_forecasting/__init__.py and exclude src/__init__.py
• smoke-tested all six installed console commands with --help