A workout deleted on Garmin's side after being linked to an activity
404s forever on get_workout_by_id, and today's fillPendingWorkouts
retries it every sync indefinitely with no user-visible feedback --
just a perpetual "1 more workout pending" nudge. Distinguishes a
definitive 404 (via garminconnect's own GarminConnectNotFoundError)
from a transient failure, and stops retrying the former.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
