create colour scheme tructure

lua/paper-tonic-modern/groups/semantic.lua

@@ -0,0 +1,9 @@
+-- Paper Tonic Modern - Semantic Highlight Groups
+-- Custom semantic captures for language-specific highlighting
+
+local colors = require('paper-tonic-modern.colors')
+
+return {
+  -- Semantic groups (to be implemented in Phase 11.7)
+  -- Custom captures like @CssClassName, @CssIdentifier, etc.
+}