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/main.py

@@ -6,7 +6,7 @@ from typing import AsyncIterator
 from fastapi import FastAPI
 
 from app.config import settings
-from app.routers import extract_router, jobs_router
+from app.routers import decode_router, extract_router, jobs_router
 from app.services import job_queue
 
 # Configure logging
@@ -36,6 +36,7 @@ app = FastAPI(
 )
 
 # Include routers
+app.include_router(decode_router)
 app.include_router(extract_router)
 app.include_router(jobs_router)
 
@@ -54,6 +55,7 @@ async def root() -> dict:
         "version": "1.0.0",
         "log_level": settings.log_level,
         "endpoints": [
+            "POST /decode/vin - VIN string decode via Gemini",
             "POST /extract - Synchronous OCR extraction",
             "POST /extract/vin - VIN-specific extraction with validation",
             "POST /extract/receipt - Receipt extraction (fuel, general)",