Sync django-migrations with the updated tutorial

[realpython-bot]

The maintenance update of Digging Deeper Into Django Migrations re-pins the tutorial to Django 6.1 / Python 3.14 and refreshes the 0001_initial.py listing, so the companion project in django-migrations/ needed to catch up. It was still a Django 2.1 / Python 3.6 project, and on Django 6.1 python manage.py makemigrations --check failed, wanting a 0003_alter_pricehistory_id migration the article never shows.

• Draft admin: https://realpython.com/pbjt/blog/post/2306/change/
• Maintenance card: https://trello.com/c/adXBejbC

What changed

• requirements.txt (new) — pinned to the article's dependencies: Django==6.1 plus its resolved deps (asgiref==3.12.1, sqlparse==0.6.0), matching how the other Django folders in this repo pin.
• README.md — installation now says Python 3.14 / Django 6.1 and installs from requirements.txt instead of pip install "Django==2.*"; the formatting note points at Ruff, which is what this repo runs.
• historical_data/migrations/0001_initial.py — regenerated on Django 6.1: models.BigAutoField for the implicit primary key, matching the listing in the updated article. This is the change that makes makemigrations --check clean again.
• historical_data/migrations/0002_switch_to_decimals.py — regenerated on Django 6.1 (content is unchanged apart from the header and generated formatting).
• manage.py, settings.py, urls.py, wsgi.py, asgi.py — brought up to the Django 6.1 startproject scaffolding: pathlib BASE_DIR, the removed USE_L10N setting dropped, STATIC_URL = "static/", the new MAILERS block, and the docs links repointed from the unsupported /en/2.1/ docs to /en/6.1/ (the same stale-2.1-docs fix the article got). asgi.py was missing and is listed in the project tree of the primer article this project is shared with. The project's original SECRET_KEY and INSTALLED_APPS are kept.
• db.sqlite3 is deliberately left as shipped: it is the database behind the article's django_migrations table, and running migrate on it applies the three new auth migrations exactly as the updated article describes.

How this was verified

On a fresh Python 3.14.6 virtualenv installed from the new requirements.txt (Django 6.1):

• python manage.py check — no issues
• python manage.py makemigrations --check --dry-run — No changes detected (it wanted a new migration before this PR)
• python manage.py migrate against the shipped db.sqlite3 — applies auth.0010/0011/0012, and a second run prints No migrations to apply., matching the article's opening transcript
• python manage.py migrate from a deleted database — full run succeeds against the default SQLite backend
• python manage.py sqlmigrate historical_data 0001 and --backwards — both produce the output the article shows for the backwards case, and the forwards CREATE TABLE matches today's Django
• python manage.py test, plus importing bitcoin_tracker.wsgi and bitcoin_tracker.asgi
• Repo gates with the pinned ruff==0.14.1: ruff format --check django-migrations and ruff check django-migrations both pass

Nothing outside django-migrations/ is touched.