fix: revert unsupported AFC config and add diagnostic logging for VIN decode (refs #231)

- Remove AutomaticFunctionCallingConfig(max_remote_calls=3) which caused
  pydantic validation error on the installed google-genai version
- Log full Gemini raw JSON response in OCR engine for debugging
- Add engine/transmission to backend raw values log
- Add hasTrim/hasEngine/hasTransmission to decode success log

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

ocr/app/engines/gemini_engine.py

@@ -398,7 +398,12 @@ class GeminiEngine:
                     vin,
                 )
 
-            logger.info("Gemini decoded VIN %s (confidence=%.2f)", vin, raw.get("confidence", 0))
+            logger.info(
+                "Gemini decoded VIN %s (confidence=%.2f) raw=%s",
+                vin,
+                raw.get("confidence", 0),
+                json.dumps(raw, default=str),
+            )
 
             return VinDecodeResult(
                 year=resolved_year if resolved_year else raw.get("year"),