Add race and station management

- races table: name, date, description, is_active
- stations table: ordered checkpoints with GPS per race
- New /api/races and /api/races/{id}/stations endpoints
- Upload now requires race + station selection; uses station GPS
  so images without GPS EXIF are accepted
- passages filtered by active race throughout
- RacePage: create races, manage stations (add/edit/delete checkpoints)
- Navbar shows active race name
- Start and finish stations created automatically per race

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

backend/Dockerfile

@@ -6,7 +6,8 @@ WORKDIR /app
 RUN apt-get update && apt-get install -y --no-install-recommends \
     libglib2.0-0 \
     libgl1 \
-    libgomp1 \
+    tesseract-ocr \
+    tesseract-ocr-eng \
     && rm -rf /var/lib/apt/lists/*
 
 COPY requirements.txt .