Add terrain workouts and GPX course support

[lookfirst]

Summary

• add selectable terrain workouts that automatically control trainer resistance from route grade
• show synchronized top-down route and elevation views with progress, grade, resistance, climbing, descending, and completed loop/trip totals
• support loop and out-and-back course models, including Granite Switchbacks, Prairie Roll, and the ten-mile Ridgeline Time Trial
• import and export standards-based GPX workouts with duplicate detection and persistent custom course storage
• save workout definitions and progress with ride sessions and preserve them through TCX import/export
• restore trainers to 10% resistance when a session ends and keep workout selection compatible with connected shift controllers
• store each bundled workout in an editable JSON definition under src/workouts

User impact

Riders can choose a course before starting, see its terrain immediately on the dashboard, and ride resistance-driven routes while tracking their position and elevation progress. The format also establishes a clean foundation for future custom workout editing and virtual shifting integration.

Validation

• bun run ci
• 176 tests passing
• TypeScript check
• production Vite build
• local browser verification of the Ridgeline Time Trial in MPH mode with no console warnings or errors