fix: use python:3.12-alpine3.21 from Docker Hub, rewrite run.sh without bashio

fichero_printer/Dockerfile

@@ -1,18 +1,18 @@
 ARG BUILD_FROM
 FROM $BUILD_FROM
 
-# System libraries: BlueZ for BLE/RFCOMM + build tools for numpy & pillow
+# BlueZ for BLE/RFCOMM + build tools for packages without binary wheels
 RUN apk add --no-cache \
+    bash \
     bluez \
     dbus \
     gcc \
     musl-dev \
     libjpeg-turbo-dev \
-    zlib-dev \
-    libffi-dev
+    zlib-dev
 
 # Install Python runtime dependencies
-RUN pip3 install --no-cache-dir --break-system-packages \
+RUN pip install --no-cache-dir \
     "bleak>=0.21" \
     "numpy" \
     "pillow" \
@@ -21,7 +21,7 @@ RUN pip3 install --no-cache-dir --break-system-packages \
     "python-multipart>=0.0.9"
 
 # Remove build-only packages to keep the image slim
-RUN apk del gcc musl-dev libffi-dev
+RUN apk del gcc musl-dev
 
 # Copy the fichero Python package into the container
 WORKDIR /app