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' };
   }