FEATURE: Add Raymarine GPX depth importer

[Krillle]

Summary

Adds a CLI importer for Raymarine GPX tracks containing depth measurements.

Changes

• Parses Raymarine WaterDepth extensions namespace-independently
• Validates coordinates, depths, XML, and timestamps
• Requires --started-at and --interval when GPX timestamps are missing
• Requires an explicit depth reference and converts measurements to waterline reference
• Reuses the existing bathymetry types, GeoJSON generation, metadata, identity, and upload reporter
• Defaults to preview mode; uploads only with explicit --upload
• Supports local GeoJSON output, distance deduplication, and point limits
• Prevents duplicate uploads with a local hash-based import ledger
• Ignores WaterTemp for now
• Adds fixtures, tests, CLI registration, and documentation

Example

npm run crowd-depth-import -- ./track.gpx \
  --depth-reference belowTransducer \
  --transducer-depth 0.45 \
  --started-at 2025-07-12T08:30:00+02:00 \
  --interval 1s \
  --dry-run \
  --out ./track.geojson

Notes

Imported GPX data is not written to the plugin’s SQLite database. Preview data remains local; with --upload, it is submitted directly through the existing API path.

No tidal or vertical-datum correction is applied. Missing heading is supported, so sensor-position correction is skipped.