Add: alpine ski waist width recommendation with terrain selector

- Add AlpineTerrain type ('groomed' | 'all-mountain' | 'powder') and
  ALPINE_TERRAIN_LABELS to types/index.ts
- Add calculateAlpineWaistWidth(terrain) to sizing.ts with documented
  ranges: 65–80 mm (groomed), 80–96 mm (all-mountain), 96–120 mm (powder)
- Add terrain selector pill row to SportSizing (alpine tab only),
  following the same pattern as the Nordic model selector
- Display 'Ski Waist' mm range in Equipment Sizing section below ski length
- Add 4 tests for calculateAlpineWaistWidth in sizing.test.ts

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: theredmoose

src/components/SportSizing.tsx

@@ -1,12 +1,13 @@
 import { useState, useRef } from 'react';
 import { ChevronLeft } from 'lucide-react';
-import type { FamilyMember, GearItem, SkillLevel, Sport, GearType, SizingModel, SizingDisplay } from '../types';
-import { SIZING_MODEL_LABELS } from '../types';
+import type { FamilyMember, GearItem, SkillLevel, Sport, GearType, SizingModel, SizingDisplay, AlpineTerrain } from '../types';
+import { SIZING_MODEL_LABELS, ALPINE_TERRAIN_LABELS } from '../types';
 import {
   calculateNordicSkiSizingByModel,
   calculateNordicBootSizing,
   calculateAlpineSkiSizing,
   calculateAlpineBootSizing,
+  calculateAlpineWaistWidth,
   calculateSnowboardSizing,
   calculateSnowboardBootSizing,
   calculateHockeySkateSize,
@@ -52,6 +53,7 @@ export function SportSizing({
   const [currentIndex, setCurrentIndex] = useState(0);
   const [sizingModel, setSizingModel] = useState<SizingModel>(defaultSizingModel);
   const [sizingDisplay, setSizingDisplay] = useState<SizingDisplay>(defaultSizingDisplay);
+  const [alpineTerrain, setAlpineTerrain] = useState<AlpineTerrain>('all-mountain');
   const [skillLevels, setSkillLevels] = useState<Record<Sport, SkillLevel>>(() => ({
     'nordic-classic': member.skillLevels?.['nordic-classic'] ?? 'intermediate',
     'nordic-skate':   member.skillLevels?.['nordic-skate']   ?? 'intermediate',
@@ -191,6 +193,7 @@ export function SportSizing({
   const renderAlpineContent = () => {
     const skiSizing  = calculateAlpineSkiSizing(member.measurements, skillLevel, member.gender);
     const bootSizing = calculateAlpineBootSizing(member.measurements, skillLevel, member.gender);
+    const waistWidth = calculateAlpineWaistWidth(alpineTerrain);
     const showRange  = sizingDisplay === 'range';
 
     return (
@@ -217,6 +220,13 @@ export function SportSizing({
                 )}
               </div>
             </div>
+            <div className="sizing-row">
+              <span className="sizing-label">Ski Waist</span>
+              <div className="sizing-value-group">
+                <span className="sizing-value">{waistWidth.min}–{waistWidth.max}</span>
+                <span className="sizing-unit">mm</span>
+              </div>
+            </div>
             <div className="sizing-row">
               <span className="sizing-label">Boots</span>
               <div className="sizing-value-group">
@@ -465,6 +475,28 @@ export function SportSizing({
           </div>
         )}
 
+        {/* Terrain selector (Alpine only) */}
+        {currentSport.id === 'alpine' && (
+          <div className="px-6 py-2 bg-slate-50 border-b border-slate-100 flex items-center gap-2">
+            <span className="text-[10px] font-black text-slate-400 uppercase tracking-widest mr-1">Terrain</span>
+            {(['groomed', 'all-mountain', 'powder'] as AlpineTerrain[]).map((t) => (
+              <button
+                key={t}
+                onClick={() => setAlpineTerrain(t)}
+                className={`px-3 py-1 rounded-lg text-[10px] font-bold border transition-colors ${
+                  alpineTerrain === t
+                    ? 'text-white border-transparent'
+                    : 'bg-white text-slate-500 border-slate-200 hover:border-slate-300'
+                }`}
+                style={alpineTerrain === t ? { backgroundColor: currentSport.color, borderColor: currentSport.color } : undefined}
+                aria-pressed={alpineTerrain === t}
+              >
+                {ALPINE_TERRAIN_LABELS[t]}
+              </button>
+            ))}
+          </div>
+        )}
+
         {/* Loadout + member info */}
         <div className="sizing-sections">
           <GearLoadoutPanel

src/services/__tests__/sizing.test.ts

@@ -4,6 +4,7 @@ import {
   calculateNordicBootSizing,
   calculateAlpineSkiSizing,
   calculateAlpineBootSizing,
+  calculateAlpineWaistWidth,
   calculateSnowboardSizing,
   calculateSnowboardBootSizing,
   calculateHockeySkateSize,
@@ -205,6 +206,37 @@ describe('sizing service', () => {
     });
   });
 
+  // ============================================
+  // ALPINE WAIST WIDTH
+  // ============================================
+  describe('calculateAlpineWaistWidth', () => {
+    it('returns 65–80 mm for groomed terrain', () => {
+      const result = calculateAlpineWaistWidth('groomed');
+      expect(result.min).toBe(65);
+      expect(result.max).toBe(80);
+    });
+
+    it('returns 80–96 mm for all-mountain terrain', () => {
+      const result = calculateAlpineWaistWidth('all-mountain');
+      expect(result.min).toBe(80);
+      expect(result.max).toBe(96);
+    });
+
+    it('returns 96–120 mm for powder terrain', () => {
+      const result = calculateAlpineWaistWidth('powder');
+      expect(result.min).toBe(96);
+      expect(result.max).toBe(120);
+    });
+
+    it('ranges are in ascending order (groomed < all-mountain < powder)', () => {
+      const groomed     = calculateAlpineWaistWidth('groomed');
+      const allMountain = calculateAlpineWaistWidth('all-mountain');
+      const powder      = calculateAlpineWaistWidth('powder');
+      expect(groomed.max).toBeLessThanOrEqual(allMountain.min);
+      expect(allMountain.max).toBeLessThanOrEqual(powder.min);
+    });
+  });
+
   // ============================================
   // SNOWBOARD SIZING
   // ============================================

src/services/sizing.ts

@@ -2,6 +2,7 @@ import type {
   Measurements,
   SkillLevel,
   SizingModel,
+  AlpineTerrain,
   NordicSkiSizing,
   NordicBootSizing,
   AlpineSkiSizing,
@@ -349,6 +350,26 @@ export function calculateAlpineSkiSizing(
   };
 }
 
+/**
+ * Recommend alpine ski waist width range based on terrain preference.
+ *
+ * Waist width (the narrowest point of the ski) is the primary driver of
+ * how a ski performs in different snow/terrain conditions:
+ *   groomed      65–80 mm  — hardpack, carving, race
+ *   all-mountain 80–96 mm  — versatile, mixed conditions
+ *   powder       96–120 mm — off-piste, soft snow, freeride
+ */
+export function calculateAlpineWaistWidth(
+  terrain: AlpineTerrain
+): { min: number; max: number } {
+  const ranges: Record<AlpineTerrain, { min: number; max: number }> = {
+    'groomed':      { min: 65,  max: 80  },
+    'all-mountain': { min: 80,  max: 96  },
+    'powder':       { min: 96,  max: 120 },
+  };
+  return ranges[terrain];
+}
+
 /**
  * Calculate DIN release setting
  * This is a simplified calculation - actual DIN should be set by a professional

src/types/index.ts

@@ -66,6 +66,15 @@ export const SIZING_MODEL_LABELS: Record<SizingModel, string> = {
   evosports: 'Evosports',
 };
 
+// Alpine terrain preference — drives waist width recommendation
+export type AlpineTerrain = 'groomed' | 'all-mountain' | 'powder';
+
+export const ALPINE_TERRAIN_LABELS: Record<AlpineTerrain, string> = {
+  'groomed':      'Groomed',
+  'all-mountain': 'All-Mountain',
+  'powder':       'Powder',
+};
+
 // Nordic Skiing
 export interface NordicSkiSizing {
   sport: 'nordic-classic' | 'nordic-skate' | 'nordic-combi';