Extract climb detection into a dedicated climb package

Move climb detection, slope, and Cotacol scoring out of ride into a new
climb package that operates on a geometry-only Route (distances, elevations,
coords). Ride embeds climb.Route and keeps its timing and telemetry columns.

- climb.Detect returns []DetectedClimb (Climb + ride-absolute Start).
- Climb owns its sliced geometry; indices are local, with Start reported at
  the detection boundary for absolute position.
- Detected bounds use core.Interval; freeRegions claim suppression fixed.
- ride no longer builds slices: ClimbFromDist/ClimbFromIndexes/climbFrom and
  ride.Climb/Interval/Range are removed; rideanalysis, mountain_pass MatchClimb,
  and web views are rewired to climb types.
- New internal/routetest builds climb.Route from the ride DSL; ridetest reuses
  it and adds timestamps and telemetry.
- Tests moved to climb (synthetic detection and difficulty) and kept in ride
  for GPX-example integration; ride.comparison detection coverage retained.
- mountain_pass.nearestCrossing now reuses geo.Nearest.

1 files changed, 72 insertions, 0 deletions

diff --git a/climb/difficulty_test.go b/climb/difficulty_test.go
new file mode 100644
index 0000000..92c0a74
--- /dev/null
+++ b/climb/difficulty_test.go
@@ -0,0 +1,72 @@
+package climb_test
+
+import (
+	"math"
+	"testing"
+
+	"github.com/martinlehoux/biking_home/climb"
+	"github.com/martinlehoux/biking_home/internal/routetest"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCotacolConstantClimb(t *testing.T) {
+	route := routetest.MustRoute("2km at 7%")
+	assert.InDelta(t, 98.0, climb.Cotacol(route.Distances, route.Elevations), 1e-9)
+}
+
+func TestCotacolIgnoresDescent(t *testing.T) {
+	route := routetest.MustRoute("2km at 7% | 2km at -7%")
+	assert.InDelta(t, 98.0, climb.Cotacol(route.Distances, route.Elevations), 1e-9)
+}
+
+func TestCotacolFlatIsZero(t *testing.T) {
+	route := routetest.MustRoute("5km at 0%")
+	assert.Zero(t, climb.Cotacol(route.Distances, route.Elevations))
+}
+
+func TestCotacolSteepShortCountsMore(t *testing.T) {
+	steep := routetest.MustRoute("0.5km at 14%")
+	long := routetest.MustRoute("1km at 7%")
+	assert.InDelta(t, 98.0, climb.Cotacol(steep.Distances, steep.Elevations), 1e-9)
+	assert.InDelta(t, 49.0, climb.Cotacol(long.Distances, long.Elevations), 1e-9)
+}
+
+func TestCotacolPrecisionInvariant(t *testing.T) {
+	coarse := routetest.MustRoute("3km at 5%")
+	fine := routetest.MustRoute("3km at 5%", routetest.Sampling(50))
+	assert.InDelta(t, climb.Cotacol(coarse.Distances, coarse.Elevations), climb.Cotacol(fine.Distances, fine.Elevations), 1e-9)
+}
+
+func TestCotacolClimbNotAtStart(t *testing.T) {
+	route := routetest.MustRoute("1km at 0% | 2km at 7%")
+	detected := climb.Detect(route, nil, climb.ClimbSlopeMinimum)
+	assert.Len(t, detected, 1)
+	assert.InDelta(t, 98.0, detected[0].Climb.DifficultyScore(), 1e-9)
+}
+
+func TestCategoryOfBoundaries(t *testing.T) {
+	cases := []struct {
+		score float64
+		want  climb.Category
+	}{
+		{-5, climb.CategoryNo},
+		{30, climb.CategoryNo},
+		{35, climb.CategoryFour}, // 35 is the first floor, not below it
+		{79, climb.CategoryFour},
+		{80, climb.CategoryThree},
+		{179, climb.CategoryThree},
+		{180, climb.CategoryTwo},
+		{249, climb.CategoryTwo},
+		{250, climb.CategoryOne},
+		{599, climb.CategoryOne},
+		{600, climb.CategoryHC},
+		{700, climb.CategoryHC},
+		{math.NaN(), climb.CategoryHC}, // reaches no floor, like the original switch default
+	}
+
+	for _, c := range cases {
+		assert.Equal(t, c.want, climb.CategoryOf(c.score), "score %v", c.score)
+	}
+	assert.Equal(t, "Cat 1", climb.CategoryOne.String())
+	assert.Equal(t, "NO", climb.CategoryNo.String())
+}