feat: add Sentinel-1 SAR support and integration tests

[rfievet]

Summary

This PR adds Sentinel-1 SAR support to complete the Copernicus Data Space Ecosystem integration. Users can now download and process both optical (S2) and radar (S1) satellite imagery.

Builds on: PR #1 (Core + S2 Basic) and PR #2 (S2 Processing)

What's New

S1 SAR Capabilities

• Download SAR data: All-weather, day/night radar imagery
• Polarization filtering: VV, VH, HH, HV modes
• Orbit filtering: ASCENDING/DESCENDING passes
• Acquisition modes: IW (default), EW, SM, WV with detailed documentation
• SAR processing: Extract backscatter composites with dB conversion
• Visualization: Display SAR imagery with interpretation guides

New Files

• src/data/copernicus/s1.py - S1 search and download logic
• tests/test_copernicus_integration.py - Integration tests for S1+S2 workflows
• scripts/download_test_data.py - Example script for downloading test data

Modified Files

• src/data/copernicus/client.py - Added fetch_s1() method
• src/data/copernicus/image_processing.py - Added extract_sar_composite()
• src/data/copernicus/visualization.py - Added display_sar_image() and create_sar_comparison_plot()
• src/data/copernicus/__init__.py - Updated exports

Usage Example

from src.data.copernicus import CopernicusClient, extract_sar_composite, display_sar_image

# Download S1 SAR data
client = CopernicusClient()
s1_files = client.fetch_s1(
    bbox=[6.15, 49.11, 6.16, 49.12],
    start_date="2024-01-01",
    end_date="2024-01-31",
    polarization="VV,VH",
    orbit_direction="ASCENDING",
    acquisition_mode="IW"  # Default: 250km coverage, 10m resolution
)

# Extract SAR backscatter
sar_data = extract_sar_composite(s1_files[0], to_db=True)
print(sar_data['polarizations'])  # ['VV', 'VH']

# Visualize
display_sar_image(s1_files[0], polarization='VV')

Why SAR Matters

Sentinel-1 SAR complements Sentinel-2 optical imagery:

• ✅ Works through clouds and rain
• ✅ Operates day and night
• ✅ Measures surface roughness and moisture
• ✅ Essential for all-weather Earth observation

Testing

All tests pass (48/48):

• PR1 tests: 18/18 ✅
• PR2 tests: 19/19 ✅
• PR3 tests: 11/11 ✅

# Run integration tests (requires test data)
uv run python scripts/download_test_data.py
uv run pytest tests/test_copernicus_integration.py -v

Complete Feature Set

The Copernicus client now supports:

• ✅ OAuth2 authentication with token refresh
• ✅ S2 optical imagery (RGB, spectral indices, cloud masking)
• ✅ S1 SAR imagery (all polarizations, modes, orbits)
• ✅ Robust download with retry and resume
• ✅ Caching for efficiency
• ✅ Memory optimization (bbox cropping)
• ✅ Comprehensive visualization
• ✅ Integration tests with real data