Replace alpine crond with supercronic

alpine crond requires root; supercronic works as any user.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -1,15 +1,16 @@
 FROM alpine:3.19
 
 # zstd for compression, tzdata so cron fires at correct local time
-RUN apk add --no-cache zstd tzdata
+RUN apk add --no-cache zstd tzdata curl
 
 COPY compress.sh /usr/local/bin/compress.sh
 RUN chmod +x /usr/local/bin/compress.sh
 
-# Install crontab: run compress at 02:00 every night
-RUN echo "0 2 * * * /usr/local/bin/compress.sh > /proc/1/fd/1 2>&1" \
-    | crontab -
+# supercronic runs as any user (unlike alpine crond which requires root)
+RUN ARCH=$(uname -m | sed 's/x86_64/amd64/;s/aarch64/arm64/') && \
+    curl -fsSL "https://github.com/aptible/supercronic/releases/latest/download/supercronic-linux-${ARCH}" \
+    -o /usr/local/bin/supercronic && chmod +x /usr/local/bin/supercronic
 
-# crond -f: foreground (required for containers)
-# crond -l 2: log level warning and above
-CMD ["crond", "-f", "-l", "2"]
+RUN echo "0 2 * * * /usr/local/bin/compress.sh > /proc/1/fd/1 2>&1" > /etc/crontab
+
+CMD ["supercronic", "/etc/crontab"]