Add IBTrACS USA wind buffers pipeline

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Summary

• Adds storms.ibtracs_wind_buffers table (one row per storm per wind speed threshold: 34/50/64 kt)
• New pipeline src/pipelines/wind_buffers.py reads USA quadrant wind radii from PROD ibtracs_tracks_geo, calls ocha-lens buffer calculation functions, and writes to DEV
• Registered as wind-buffers subcommand in run_pipeline.py with optional --basin and --start-year filters

Depends on the usa-wind-buffers PR in ocha-lens being merged first (for calculate_wind_buffers_gdf and expand_quad_col).

Usage

# Full historical run
python run_pipeline.py wind-buffers --mode dev

# Subset (e.g. for testing)
python run_pipeline.py wind-buffers --mode dev --basin NA --start-year 2020

Test plan

• Tested NA basin since 2020 against DEV DB (135 storms, 405 buffer polygons written successfully)
• Run SQL schema against target DB before first run
• Run full historical backfill once ocha-lens PR is merged and version bumped in requirements.txt

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Superseded by #15.

All commits on this branch (72687de, 7a7e9e7, 5b5bdcf, README updates) were merged into wsp-adm0-exp via merge commit e9239f9, and the standalone src/pipelines/wind_buffers.py was later folded into src/pipelines/ibtracs.py and src/pipelines/nhc.py (commit 49dd298). The IBTrACS + NHC wind-buffer pipelines now ship as part of #15 alongside the full exposure cascade and Databricks bundle.

Closing — please review there.