fix: align VIN OCR logging with unified logging design (refs #113)

Replace filesystem-based debug system (VIN_DEBUG_DIR) with standard
logger.debug() calls that flow through Loki when LOG_LEVEL=DEBUG.
Use .env.logging variable for OCR LOG_LEVEL. Increase image capture
quality to 0.95 for better OCR accuracy.

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

docker-compose.yml

@@ -187,7 +187,7 @@ services:
     container_name: mvp-ocr
     restart: unless-stopped
     environment:
-      LOG_LEVEL: info
+      LOG_LEVEL: ${BACKEND_LOG_LEVEL:-info}
       REDIS_HOST: mvp-redis
       REDIS_PORT: 6379
       REDIS_DB: 1

frontend/src/shared/components/CameraCapture/useImageCrop.ts

@@ -304,7 +304,7 @@ export function useImageCrop(options: UseImageCropOptions = {}): UseImageCropRet
               }
             },
             mimeType,
-            0.92
+            0.95
           );
         };
 

ocr/app/extractors/vin_extractor.py

@@ -89,15 +89,26 @@ class VinExtractor(BaseExtractor):
             )
 
         try:
+            logger.debug(
+                "VIN extraction input: %d bytes, content_type=%s",
+                len(image_bytes), content_type,
+            )
+
             # Apply VIN-optimized preprocessing
             preprocessing_result = vin_preprocessor.preprocess(image_bytes)
             preprocessed_bytes = preprocessing_result.image_bytes
+            logger.debug(
+                "Preprocessing steps: %s", preprocessing_result.preprocessing_applied
+            )
 
             # Perform OCR with VIN-optimized settings
             raw_text, word_confidences = self._perform_ocr(preprocessed_bytes)
+            logger.debug("PSM 6 raw text: '%s'", raw_text)
+            logger.debug("PSM 6 word confidences: %s", word_confidences)
 
             # Extract VIN candidates from raw text
             candidates = vin_validator.extract_candidates(raw_text)
+            logger.debug("PSM 6 candidates: %s", candidates)
 
             if not candidates:
                 # No VIN candidates found - try with different PSM modes
@@ -106,12 +117,22 @@ class VinExtractor(BaseExtractor):
             if not candidates:
                 # Try alternative preprocessing (Otsu's thresholding)
                 otsu_result = vin_preprocessor.preprocess_otsu(image_bytes)
+                logger.debug(
+                    "Otsu preprocessing steps: %s",
+                    otsu_result.preprocessing_applied,
+                )
+
                 raw_text, word_confidences = self._perform_ocr(otsu_result.image_bytes)
+                logger.debug("Otsu PSM 6 raw text: '%s'", raw_text)
                 candidates = vin_validator.extract_candidates(raw_text)
+                logger.debug("Otsu PSM 6 candidates: %s", candidates)
                 if not candidates:
-                    candidates = self._try_alternate_ocr(otsu_result.image_bytes)
+                    candidates = self._try_alternate_ocr(
+                        otsu_result.image_bytes, prefix="Otsu"
+                    )
 
             if not candidates:
+                logger.debug("No VIN pattern found in any OCR attempt")
                 return VinExtractionResult(
                     success=False,
                     error="No VIN pattern found in image",
@@ -161,8 +182,12 @@ class VinExtractor(BaseExtractor):
             processing_time_ms = int((time.time() - start_time) * 1000)
 
             logger.info(
-                f"VIN extraction: {primary_vin}, confidence={primary_confidence:.2%}, "
+                "VIN extraction: %s, confidence=%.2f%%, time=%dms",
-                f"time={processing_time_ms}ms"
+                primary_vin, primary_confidence * 100, processing_time_ms,
+            )
+            logger.debug(
+                "VIN alternatives: %s",
+                [(a.vin, a.confidence) for a in alternatives],
             )
 
             return VinExtractionResult(
@@ -176,7 +201,7 @@ class VinExtractor(BaseExtractor):
             )
 
         except Exception as e:
-            logger.error(f"VIN extraction failed: {e}", exc_info=True)
+            logger.error("VIN extraction failed: %s", e, exc_info=True)
             return VinExtractionResult(
                 success=False,
                 error=str(e),
@@ -236,7 +261,11 @@ class VinExtractor(BaseExtractor):
         raw_text = " ".join(words)
         return raw_text, confidences
 
-    def _try_alternate_ocr(self, image_bytes: bytes) -> list[tuple[str, int, int]]:
+    def _try_alternate_ocr(
+        self,
+        image_bytes: bytes,
+        prefix: str = "",
+    ) -> list[tuple[str, int, int]]:
         """
         Try alternate OCR configurations when initial extraction fails.
 
@@ -249,9 +278,12 @@ class VinExtractor(BaseExtractor):
         Returns:
             List of VIN candidates
         """
+        tag = f"{prefix} " if prefix else ""
         for psm in (7, 8, 11, 13):
             raw_text, _ = self._perform_ocr(image_bytes, psm=psm)
+            logger.debug("%sPSM %d raw text: '%s'", tag, psm, raw_text)
             candidates = vin_validator.extract_candidates(raw_text)
+            logger.debug("%sPSM %d candidates: %s", tag, psm, candidates)
             if candidates:
                 return candidates