add ROM file selection to upgrade dialog

[noahlemen]

use case

allows upgrading to arbitrary lsdj version instead of latest experimental or stable (e.g., 4.7.3 to 5.0.3) while preserving custom kits, fonts, and palettes.

testing

successfully tested upgrading from patched lsdj 7.0.2 to 9.4.0 with custom sample kits, verified that custom sample kits persisted

note: palette count mismatches between ROM versions can cause import to fail. in my actual use case (4.7.3 to 5.0.3), i temporarily commented out the palette import check to complete the upgrade. future enhancement could make palette import optional when count mismatches are detected.

changes

• adds "Select ROM file..." button to ROM upgrade dialog
• validates file size matches expected ROM size
• reuses existing import logic for kits, fonts, and palettes

[jkotlinski]

Looks good! Thank you for contributing!