docs: add reproducible Python 3.11.13 setup

[VolodymyrLinuxovich]

Summary

Adds a reproducible setup path using the Python version already pinned in
.python-version.

Problem

The README currently specifies Python 3.11+ and creates the virtual environment
using the user's default python executable. On systems where another
interpreter is the default, that setup does not reproduce the repository's
pinned Python environment.

Changes

• Recommend Python 3.11.13, matching .python-version.
• Add a uv setup path that installs and selects Python 3.11.13 explicitly.
• Add a Python version verification step.
• Retain the existing standard venv and pip setup as an alternative.

Validation

Followed the new instructions from a clean temporary environment on macOS:

uv python install 3.11.13
uv venv --python 3.11.13
source .venv/bin/activate
python --version
uv pip install -r requirements.txt

Result:

Python 3.11.13
All dependency imports succeeded.

Also ran git diff --check successfully.

Closes #398