SCSS Path resolution fix

[spinboxnl]

The SCSS path resolution didn't work properly and it removed underscores where it shouldn't.

Fixed path resolution by:

• Sorting includePaths longest‑first (most specific wins consistently).
• Adding a computed common root to setImportPaths() so master imports can resolve across sibling folders.
• Generating @import paths relative to the most specific includePath, falling back to the common root, and finally to the basename.
• Stripping .scss and a leading _ on the basename only.
• Normalizing path separators.