Improve “Fundamental Concepts” Tutorial and Screenshot Organization

[cmarteepants]

Summary

This PR improves the Airflow "Fundamental Concepts" tutorial by rewriting for better clarity, structure, and tone. It also updates screenshots for Airflow 3.

Related:

• High Priority Airflow-Core Doc Updates for 3.0.0 Release #45649
• Update README and docs with Airflow 3 UI screenshots #48785

What's Included

• Rewrites the Fundamental Concepts tutorial to be more conversational and beginner-friendly, while maintaining all technical accuracy and code examples
• Updates screenshots to reflect the UI (😈 )
• Adds screenshots for light mode too in case we move to a docs theme that supports light and dark mode
• Groups screenshots by light and dark theme for organizational purposes

Why This Matters

The existing tutorial content was technically accurate but written in a style that could be intimidating or confusing for newcomers. This update provides a more natural learning path for users familiar with Python but new to Airflow, helping them build confidence as they go. Also: We need to update screenshots for Airflow 3 😄 and since I was there, I couldn't help but adjust it.

[jason810496]

Thanks for the change! Looks great!
However, the static check isn’t happy — we need to use double backticks for code blocks to fix it.

Check if RST files use double backticks for code............................Failed
- hook id: rst-backticks
- exit code: 1

airflow-core/docs/tutorial/fundamentals.rst:83:`dag_id`, and specify the default arguments we just defined. We'll also set a schedule for our DAG to run every day.
airflow-core/docs/tutorial/fundamentals.rst:146:`{{ ds }}`. You can also pass files to the ``bash_command``, such as ``bash_command='templated_command.sh'``, allowing
airflow-core/docs/tutorial/fundamentals.rst:176:In Airflow, tasks can depend on one another. For instance, if you have tasks `t1`, `t2`, and `t3`, you can defined their
airflow-core/docs/tutorial/fundamentals.rst:232:`tutorial.py` within the dags folder specified in your ``airflow.cfg``, you can run:

[cmarteepants]

Thanks @jason810496! On me. I ran pre-commit manually before submitting the PR, but didn't verify with breeze. Pushed it through, hopefully the static tests pass.