Roundcube as its own image built by the workflow (no config file or newer Compose needed)

- roundcube/: official Roundcube plus hub.php settings
- workflow builds and pushes git.necloud.us/nate/hub-roundcube, and runs the player and webmail tests
- compose uses the image instead of an inline config

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

roundcube/Dockerfile

@@ -0,0 +1,7 @@
+# Roundcube webmail for NE Hub: the official image plus the hub's settings (so no config file has to be mounted).
+FROM roundcube/roundcubemail:latest-apache
+COPY hub.php /var/roundcube/config/hub.php
+ENV ROUNDCUBEMAIL_DB_TYPE=sqlite \
+    ROUNDCUBEMAIL_REQUEST_PATH=/webmail/ \
+    ROUNDCUBEMAIL_PLUGINS=archive,zipdownload \
+    ROUNDCUBEMAIL_UPLOAD_MAX_FILESIZE=30M