Fix Docker build context paths and add runtime API URL configuration

Co-authored-by: johndoe6345789 <224850594+johndoe6345789@users.noreply.github.com>

backend/Dockerfile

@@ -3,14 +3,14 @@ FROM python:3.11-slim
 WORKDIR /app
 
 # Install dependencies
-COPY requirements.txt .
+COPY backend/requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
 
 # Copy application files
-COPY app.py auth.py ./
+COPY backend/app.py backend/auth.py backend/config_db.py ./
 
 # Copy schema from parent directory
-COPY ../schema.json /app/schema.json
+COPY schema.json /app/schema.json
 
 # Create data directory
 RUN mkdir -p /data/blobs /data/meta