refactor: Use single table for colorscheme variants

Author: reobin

db/migrations/20251005195216_colorschemes.sql

@@ -1,15 +1,9 @@
-CREATE TABLE colorschemes (
-  name TEXT NOT NULL,
-  repository_id INTEGER NOT NULL REFERENCES repositories(id) ON DELETE CASCADE,
-
-  PRIMARY KEY (name, repository_id)
-);
-
-CREATE TABLE colorscheme_color_data (
+CREATE TABLE colorscheme_variants (
   colorscheme_name TEXT NOT NULL,
   repository_id INTEGER NOT NULL REFERENCES repositories(id) ON DELETE CASCADE,
   background TEXT NOT NULL CHECK (background IN ('light', 'dark')),
   color_data JSON NOT NULL,
 
   PRIMARY KEY (colorscheme_name, repository_id, background)
+  FOREIGN KEY (colorscheme_name, repository_id) REFERENCES colorschemes(name, repository_id) ON DELETE CASCADE
 )