feat: Add fuzzy matching to VIN decode for partial model/trim names (refs #9)

Backend: Enhanced matchField function with prefix and contains matching
so NHTSA values like "Sierra" match dropdown options like "Sierra 1500".

Matching hierarchy:
1. Exact match (case-insensitive) -> high confidence
2. Normalized match (remove special chars) -> medium confidence
3. Prefix match (option starts with value) -> medium confidence (NEW)
4. Contains match (option contains value) -> medium confidence (NEW)

Frontend: Fixed VIN decode form population by loading dropdown options
before setting form values, preventing cascade useEffects from clearing
decoded values.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/features/vehicles/domain/vehicles.service.ts

@@ -441,8 +441,9 @@ export class VehiclesService {
   }
 
   /**
-   * Match a value against dropdown options using case-insensitive exact matching
+   * Match a value against dropdown options using fuzzy matching
    * Returns the matched dropdown value with confidence level
+   * Matching order: exact -> normalized -> prefix -> contains
    */
   private matchField(nhtsaValue: string, options: string[]): MatchedField<string> {
     if (!nhtsaValue || options.length === 0) {
@@ -466,6 +467,18 @@ export class VehiclesService {
       return { value: normalizedMatch, nhtsaValue, confidence: 'medium' };
     }
 
+    // Try prefix match - option starts with NHTSA value
+    const prefixMatch = options.find(opt => opt.toLowerCase().trim().startsWith(normalizedNhtsa));
+    if (prefixMatch) {
+      return { value: prefixMatch, nhtsaValue, confidence: 'medium' };
+    }
+
+    // Try contains match - option contains NHTSA value
+    const containsMatch = options.find(opt => opt.toLowerCase().trim().includes(normalizedNhtsa));
+    if (containsMatch) {
+      return { value: containsMatch, nhtsaValue, confidence: 'medium' };
+    }
+
     // No match found - return NHTSA value as hint with no match
     return { value: null, nhtsaValue, confidence: 'none' };
   }

frontend/src/features/vehicles/components/VehicleForm.tsx

@@ -448,13 +448,45 @@ export const VehicleForm: React.FC<VehicleFormProps> = ({
       isVinDecoding.current = true;
       setLoadingDropdowns(true);
 
-      // Track which values we're setting (only populate empty fields)
+      // Determine final values (decoded value if field is empty, otherwise keep existing)
-      const yearToSet = !watchedYear && decoded.year.value ? decoded.year.value : watchedYear;
+      const yearValue = !watchedYear && decoded.year.value ? decoded.year.value : watchedYear;
-      const makeToSet = !watchedMake && decoded.make.value ? decoded.make.value : watchedMake;
+      const makeValue = !watchedMake && decoded.make.value ? decoded.make.value : watchedMake;
-      const modelToSet = !watchedModel && decoded.model.value ? decoded.model.value : watchedModel;
+      const modelValue = !watchedModel && decoded.model.value ? decoded.model.value : watchedModel;
-      const trimToSet = !watchedTrim && decoded.trimLevel.value ? decoded.trimLevel.value : watchedTrim;
+      const trimValue = !watchedTrim && decoded.trimLevel.value ? decoded.trimLevel.value : watchedTrim;
+      const engineValue = !watchedEngine && decoded.engine.value ? decoded.engine.value : watchedEngine;
+      const transmissionValue = !watchedTransmission && decoded.transmission.value ? decoded.transmission.value : watchedTransmission;
 
-      // Set form values
+      // FIRST: Load all dropdown options hierarchically (like edit mode initialization)
+      // Options must exist BEFORE setting form values for selects to display correctly
+      if (yearValue) {
+        prevYear.current = yearValue;
+        const makesData = await vehiclesApi.getMakes(yearValue);
+        setMakes(makesData);
+
+        if (makeValue) {
+          prevMake.current = makeValue;
+          const modelsData = await vehiclesApi.getModels(yearValue, makeValue);
+          setModels(modelsData);
+
+          if (modelValue) {
+            prevModel.current = modelValue;
+            const trimsData = await vehiclesApi.getTrims(yearValue, makeValue, modelValue);
+            setTrims(trimsData);
+
+            if (trimValue) {
+              prevTrim.current = trimValue;
+              const [enginesData, transmissionsData] = await Promise.all([
+                vehiclesApi.getEngines(yearValue, makeValue, modelValue, trimValue),
+                vehiclesApi.getTransmissions(yearValue, makeValue, modelValue, trimValue)
+              ]);
+              setEngines(enginesData);
+              setTransmissions(transmissionsData);
+            }
+          }
+        }
+      }
+
+      // THEN: Set form values (after options are loaded)
       if (!watchedYear && decoded.year.value) {
         setValue('year', decoded.year.value);
       }
@@ -474,36 +506,6 @@ export const VehicleForm: React.FC<VehicleFormProps> = ({
         setValue('transmission', decoded.transmission.value);
       }
 
-      // Load dropdown options hierarchically (like edit mode initialization)
-      // This ensures dropdowns have the right options for the decoded values
-      if (yearToSet) {
-        prevYear.current = yearToSet;
-        const makesData = await vehiclesApi.getMakes(yearToSet);
-        setMakes(makesData);
-
-        if (makeToSet) {
-          prevMake.current = makeToSet;
-          const modelsData = await vehiclesApi.getModels(yearToSet, makeToSet);
-          setModels(modelsData);
-
-          if (modelToSet) {
-            prevModel.current = modelToSet;
-            const trimsData = await vehiclesApi.getTrims(yearToSet, makeToSet, modelToSet);
-            setTrims(trimsData);
-
-            if (trimToSet) {
-              prevTrim.current = trimToSet;
-              const [enginesData, transmissionsData] = await Promise.all([
-                vehiclesApi.getEngines(yearToSet, makeToSet, modelToSet, trimToSet),
-                vehiclesApi.getTransmissions(yearToSet, makeToSet, modelToSet, trimToSet)
-              ]);
-              setEngines(enginesData);
-              setTransmissions(transmissionsData);
-            }
-          }
-        }
-      }
-
       setLoadingDropdowns(false);
       isVinDecoding.current = false;
     } catch (error: any) {