feat: support GRAV_CHANNEL_SUFFIX for Grav 2.0 RC production install

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

scripts/server-install.sh

@@ -11,6 +11,9 @@ set -e
 : "${GITEA_USER:?GITEA_USER is not set}"
 : "${GITEA_TOKEN:?GITEA_TOKEN is not set}"
 
+# GRAV_CHANNEL_SUFFIX: optional, set to '?testing' for RC/beta releases (e.g. 2.0.0-rc.9)
+# Leave unset or empty for stable releases.
+
 trap 'rm -f ~/.netrc' EXIT
 
 echo "==> Setting up credentials (temporary)"
@@ -19,7 +22,7 @@ chmod 600 ~/.netrc
 
 echo "==> Downloading Grav $GRAV_VERSION"
 cd "$WEBROOT"
-wget --no-verbose "https://getgrav.org/download/core/grav-admin/$GRAV_VERSION" -O grav-admin.zip
+wget --no-verbose "https://getgrav.org/download/core/grav-admin/${GRAV_VERSION}${GRAV_CHANNEL_SUFFIX:-}" -O grav-admin.zip
 unzip -oq grav-admin.zip
 cp -rf grav-admin/. .
 rm -rf grav-admin grav-admin.zip