feat: add VIN decode endpoint to OCR Python service (refs #224)

Add POST /decode/vin endpoint using Gemini 2.5 Flash for VIN string
decoding. Returns structured vehicle data (year, make, model, trim,
body/drive/fuel type, engine, transmission) with confidence score.

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

ocr/app/models/schemas.py

@@ -169,3 +169,30 @@ class ManualJobResponse(BaseModel):
     error: Optional[str] = None
 
     model_config = {"populate_by_name": True}
+
+
+class VinDecodeRequest(BaseModel):
+    """Request body for VIN decode endpoint."""
+
+    vin: str
+
+
+class VinDecodeResponse(BaseModel):
+    """Response from VIN decode endpoint."""
+
+    success: bool
+    vin: str
+    year: Optional[int] = None
+    make: Optional[str] = None
+    model: Optional[str] = None
+    trim_level: Optional[str] = Field(default=None, alias="trimLevel")
+    body_type: Optional[str] = Field(default=None, alias="bodyType")
+    drive_type: Optional[str] = Field(default=None, alias="driveType")
+    fuel_type: Optional[str] = Field(default=None, alias="fuelType")
+    engine: Optional[str] = None
+    transmission: Optional[str] = None
+    confidence: float = Field(ge=0.0, le=1.0)
+    processing_time_ms: int = Field(alias="processingTimeMs")
+    error: Optional[str] = None
+
+    model_config = {"populate_by_name": True}