DiscHarrowSettings v3 shop config fix

Important: keep the ZIP name as FS25_DiscHarrowSettings.zip.
The XML config root is tied to the mod name, so renaming the zip/folder can stop the store configuration from appearing.

Changes in v3:
- More flexible Disc Harrow category detection: DISCHARROWS, DISC_HARROWS, Disc Harrows, etc.
- Still attaches to Cultivator specialization because FS25 disc harrows generally use vehicle.cultivator internally.
- Store config applies only to disc harrow category/items, not all cultivators.
- Switchable mode save fixed to save config 5.
