Add materials, exam images, storage quota, and API guide

Upload documents for AI context, exam images for Moodle questions, per-template storage limits, embedded images in XML export, and GUIA_API_Y_FLUJO.md with full endpoint documentation.

backend/Dockerfile

@@ -5,6 +5,13 @@ ENV PYTHONDONTWRITEBYTECODE=1 \
 
 WORKDIR /app
 
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends \
+        tesseract-ocr \
+        tesseract-ocr-spa \
+        tesseract-ocr-eng \
+    && rm -rf /var/lib/apt/lists/*
+
 RUN addgroup --system app && adduser --system --ingroup app app
 
 COPY requirements.txt .
@@ -12,6 +19,8 @@ RUN pip install --no-cache-dir -r requirements.txt
 
 COPY app ./app
 
+RUN mkdir -p /app/uploads && chown -R app:app /app/uploads
+
 USER app
 
 EXPOSE 8000