fix: fetch all remote branches before checkout on reinstall

Single-branch clones only track one branch. Reset the remote refspec
to '*' before fetching so any target branch can be checked out.

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

install.sh

@@ -431,6 +431,7 @@ if [[ -d "$INSTALL_DIR/.git" ]]; then
     # safe.directory nötig wenn das Verzeichnis einem anderen User gehört
     # (z.B. ripster-Serviceuser nach erstem Install)
     git config --global --add safe.directory "$INSTALL_DIR" 2>/dev/null || true
+    git -C "$INSTALL_DIR" remote set-branches origin '*'
     git -C "$INSTALL_DIR" fetch --quiet origin
     git -C "$INSTALL_DIR" checkout --quiet -B "$GIT_BRANCH" "origin/$GIT_BRANCH"
     git -C "$INSTALL_DIR" reset --hard "origin/$GIT_BRANCH"