🖋️ Scribe: Fix broken Airflow installation instructions

[fderuiter]

💡 What: Updated README.md and docs/airflow.rst to replace the pip install "imednet[airflow]" command with explicit instructions to manually install apache-airflow and apache-airflow-providers-amazon.

🎯 Why: The airflow extra in pyproject.toml is broken because it references dependencies that are not in the main dependency list (due to version conflicts with dev dependencies). Installing imednet[airflow] currently does not install the required Airflow packages, leading to a confusing onboarding experience where users think they have installed the integration but haven't.

🧠 Cognitive Impact: Fixes a "broken path" for users trying to use Airflow features. By providing a working installation command, we reduce the time users spend debugging why imports are failing despite following the instructions.

📖 Preview:

# For Airflow integration (must be installed manually due to version conflicts)
pip install imednet apache-airflow apache-airflow-providers-amazon

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PR created automatically by Jules for task 2046806954395008790 started by @fderuiter

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