Add introductory k-space basics tutorial for MRI reconstruction

Summary

Adds a beginner-friendly introductory tutorial for MRI reconstruction using the fastMRI knee single-coil dataset and MONAI's reconstruction transforms.

Changes

• New notebook: reconstruction/MRI_reconstruction/tutorials/01_kspace_basics_fastmri_knee.ipynb
  • Part 1: What is k-space (loading real data, inverse FFT)
  • Part 2: Fourier transform connection (low vs. high frequencies)
  • Part 3: Undersampling and aliasing artifacts (1x, 2x, 4x, 8x)
  • Part 4: Random vs. equispaced masks using RandomKspaceMaskd / EquispacedKspaceMaskd
  • Part 5: Full MONAI preprocessing pipeline (FastMRIReader → CenterSpatialCropd → ReferenceBasedNormalizeIntensityd)
  • Part 6: Zero-filled reconstruction → deep learning connection
• New README: reconstruction/MRI_reconstruction/tutorials/README.md
• Updated README.md: Added missing Reconstruction section listing this tutorial plus existing unet_demo and varnet_demo
• Updated runner.sh: Added notebook to doesnt_contain_max_epochs (no training loop)

Dataset

• Uses fastMRI knee single-coil validation set (non-commercial license)
• Only one .h5 file (~300 MB) required — no need for the full ~1.5 TB brain multi-coil download
• Added to skip_run_papermill via existing .*MRI_reconstruction.* pattern

Design decisions

• Bridges the gap between newcomers and production tutorials (unet_demo, varnet_demo)
• Uses CenterSpatialCropd instead of ReferenceBasedSpatialCropd to handle the k-space (640×368) vs ground truth (320×320) dimension mismatch
• No training loop — purely educational, runs without GPU

Test plan

• Notebook runs end-to-end on Google Colab with real fastMRI knee data (file1000000.h5)
• All 5 matplotlib visualizations render correctly
• Pipeline output shapes: kspace_masked_ifft and reconstruction_esc both (1, 320, 320)
• PEP 8 passes via ./runner.sh -t reconstruction/MRI_reconstruction/tutorials/01_kspace_basics_fastmri_knee.ipynb --no-run
• Copyright header present with correct formatting

Bắt đầu với reconstruction/MRI_reconstruction/tutorials/01_kspace_basics_fastmri_knee.ipynb và so sánh nó với các tutorial unet_demo và varnet_demo hiện có. Chạy ./runner.sh -t reconstruction/MRI_reconstruction/tutorials/01_kspace_basics_fastmri_knee.ipynb --no-run, sau đó xác thực notebook bằng tệp fastMRI file1000000.h5 trong Colab. Được xem là hoàn tất khi các hình trực quan được render, các shape đầu ra được nêu khớp nhau và các mục trong README và runner.sh được cập nhật.