feat: rewire vehicles controller to OCR VIN decode (refs #226)

Replace NHTSAClient with OcrClient in vehicles controller. Move cache
logic into VehiclesService with format-aware reads (Gemini vs legacy
NHTSA entries). Rename nhtsaValue to sourceValue in MatchedField.
Remove vpic config from Zod schema and YAML config files.

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

config/shared/production.yml

@@ -107,9 +107,6 @@ external_services:
   google_maps:
     base_url: https://maps.googleapis.com/maps/api
 
-  vpic:
-    base_url: https://vpic.nhtsa.dot.gov/api/vehicles
-
 # Development Configuration
 development:
   debug_enabled: false