[Londopy]

Summary

• Adds native drag-and-drop support for .rhs skin files (the format used by the original Rhythia/Sound Space)
• Extracts cursor, grid, note skin textures, colorset, hit sound, and composites multi-layer backgrounds automatically
• New RhsImporter class handles all conversion from the .rhs zip format to the Client's skin folder layout

How it works

Drop any .rhs file onto the game window. The importer:

1. Reads the JSON config and extracts skin assets (cursor, border/grid, note skin)
2. Extracts colorset to colorsets/{skinName}.txt
3. Composites background layers (with canvas color, position, scale, fit mode, tint) into a single game/background.png
4. Extracts hit sound as hit.mp3
5. Writes a config.toml with theme color, note colors, mesh type, and sets game_space = "void" for background display
6. Registers the skin and switches to it immediately

Test plan

• Drop a .rhs skin file onto the game window — skin should import and activate
• Verify cursor, grid, colors, hit sound, and background all load correctly
• Drop multiple .rhs files — each should import without conflicts
• Drop a skin with the same name as an existing one — should overwrite cleanly