Install anipy-cli in Docker image

Install anipy-cli systemwide during the Docker build so fallback downloads work inside the container without extra setup, and update the README to describe the new Docker behavior.

Dockerfile

@@ -48,6 +48,9 @@ RUN curl -fL "${YT_DLP_RELEASE_URL}" -o /usr/local/bin/yt-dlp \
     && chmod 0755 /usr/local/bin/yt-dlp \
     && yt-dlp --version
 
+RUN python3 -m pip install --no-cache-dir anipy-cli \
+    && anipy-cli --version
+
 RUN git clone --depth 1 --branch "${ANI_CLI_WEB_BRANCH}" "${ANI_CLI_WEB}" /app \
     && rm -rf /app/.git \
     && rm -f \