Wraps @garmin/fitsdk to emit FIT Course files from GPX, the binary
format Wahoo's POST /v1/routes API requires. Server-side only — the
~1 MB SDK never ships to the planner browser bundle.
Round-trip tests use fit-file-parser as an independent oracle and
assert lat/lon parity within 1e-4 deg and altitude within 0.5 m
across short flat, alpine, multi-day, and single-point fixtures.
Updates design.md decision #1: the original hand-rolled-encoder plan
was justified largely by ESM friction in the Garmin SDK, but as of
v21.202.0 the SDK is pure ESM with zero deps. Wrapping it saves us
~400 LOC of binary plumbing and ongoing maintenance against future
FIT spec updates.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
