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/app/ci.yml

@@ -22,11 +22,6 @@ platform:
       url: http://mvp-platform-vehicles-api:8000
       timeout: 5s
 
-external:
-  vpic:
-    url: https://vpic.nhtsa.dot.gov/api/vehicles
-    timeout: 10s
-
 service:
   name: mvp-backend