Improve branch checkout fallback in update-Nitrov3.sh

Add fallback logic to try capitalized branch name if the
specified branch is not found, with a clear error message
if neither exists.

update-Nitrov3.sh

@@ -244,7 +244,15 @@ git_update() {
     git stash --include-untracked || true
     local old_head
     old_head=$(git rev-parse HEAD)
-    git checkout "$branch"
+    if ! git checkout "$branch" 2>/dev/null; then
+        local alt="${branch^}"
+        if [ "$alt" != "$branch" ] && git checkout "$alt" 2>/dev/null; then
+            info "Branch '$branch' not found, using '$alt' instead"
+            branch="$alt"
+        else
+            die "Branch '$branch' (or '$alt') not found in $repo"
+        fi
+    fi
     git pull
     [ "$(git rev-parse HEAD)" != "$old_head" ]
 }