use local timezone in log messages; closes #96

timezone can be changed with `export TZ=Europe/Oslo` before launch

using naive timestamps like this appears to be safe as of 3.13-rc1,
no deprecation warnings, just a tiny bit slower than assuming UTC

scripts/docker/Dockerfile.ac

@@ -8,7 +8,7 @@ LABEL   org.opencontainers.image.url="https://github.com/9001/copyparty" \
 ENV     XDG_CONFIG_HOME=/cfg
 
 RUN     apk --no-cache add !pyc \
-            wget \
+            tzdata wget \
             py3-jinja2 py3-argon2-cffi py3-pillow \
             ffmpeg