Passing custom targets as props invalidates [data-f1] targets

I found with the recent change I made that passing custom targets overwrites any of the targets react-f1 would have found with the data-f1 prop. You can get around this by passing those targets to the targets prop object using `refs`.

Not ideal however. I'd like to look into having the custom targets list merge with the generated list somehow.

Start by tracing how the React component handles the custom targets prop, especially its refs object, and how targets discovered through the data-f1 prop are collected. Confirm the current overwrite behavior, then verify that custom and generated target lists are both retained without breaking existing target selection.

Written by the indexing model from the issue text.