Add Docker branch selector for ani-cli-web

Add an  build argument to the Docker image so the cloned ani-cli-web source can come from a selected branch, and document the new build option in the README.

Dockerfile

@@ -3,12 +3,14 @@ FROM python:3.12-slim
 ARG ANI_CLI=https://github.com/pystardust/ani-cli.git
 ARG ANI_CLI_BRANCH=master
 ARG ANI_CLI_WEB=https://gitea.coreplay.eu/Dymas/ani-cli-web.git
+ARG ANI_CLI_WEB_BRANCH=main
 ARG YT_DLP_RELEASE_URL=https://github.com/yt-dlp/yt-dlp/releases/latest/download/yt-dlp
 
 ENV DEBIAN_FRONTEND=noninteractive \
     ANI_CLI_REPO=${ANI_CLI} \
     ANI_CLI_BRANCH=${ANI_CLI_BRANCH} \
     ANI_CLI_WEB_REPO=${ANI_CLI_WEB} \
+    ANI_CLI_WEB_BRANCH=${ANI_CLI_WEB_BRANCH} \
     ANI_CLI_BIN=ani-cli \
     ANI_CLI_DOWNLOAD_DIR=/downloads \
     ANI_CLI_WEB_HOST=0.0.0.0 \
@@ -46,7 +48,7 @@ RUN curl -fL "${YT_DLP_RELEASE_URL}" -o /usr/local/bin/yt-dlp \
     && chmod 0755 /usr/local/bin/yt-dlp \
     && yt-dlp --version
 
-RUN git clone --depth 1 "${ANI_CLI_WEB}" /app \
+RUN git clone --depth 1 --branch "${ANI_CLI_WEB_BRANCH}" "${ANI_CLI_WEB}" /app \
     && rm -rf /app/.git \
     && rm -f \
         /app/.dockerignore \

README.md

@@ -59,6 +59,14 @@ Build:
 docker build -t ani-cli-web .
 ```
 
+Build a specific `ani-cli-web` branch:
+
+```sh
+docker build \
+  --build-arg ANI_CLI_WEB_BRANCH=anipy_backup \
+  -t ani-cli-web .
+```
+
 Run:
 
 ```sh
@@ -84,6 +92,7 @@ Docker notes:
 - App state is stored under `/app/.ani-cli-web`
 - `USER_UID` and `USER_GID` help keep mounted files owned by your host user
 - `UPDATE_ON_START=true` runs `ani-cli --update` before startup
+- `ANI_CLI_WEB_BRANCH` lets the image clone a specific `ani-cli-web` branch at build time
 
 ## Key behavior