Fixed
- Course ratings (course rating and slope) are now checked to make sure they are valid numbers before saving. This prevents a crash in the handicap calculation if an invalid value ever slipped through, such as from a bad AI ratings lookup.
- Linking two nine-hole halves into one course no longer risks silently merging an unrelated existing course's rounds and ratings into the group if the names happened to match.
Both are internal safety fixes with no change to how the app is used day to day.