Compute Per-Pixel Median Composite

[RobinGummels]

Description:
Implement Step 5: Compute the median value per pixel and per band across all available Sentinel-2 scenes within the month to reduce measurement noise and cloud contamination.

Tasks:

• Stack all reprojected scenes along time dimension
• Compute median using xarray.DataArray.median(dim='time')
• Handle potential NaN values (clouds, no-data)
• Apply median computation to both B03 and B11 bands
• Verify output is a single composite image per band
• Implement cloud masking if available from SCL (Scene Classification Layer)

Acceptance Criteria:

• One median composite image per band (B03, B11)
• Cloud-contaminated pixels are properly handled
• Output has same spatial extent as candidate cell
• Visual inspection confirms cloud reduction