fix: resolve test failures for theme builder integration

- Replace hardcoded text-white and text-red-* with CSS variables in theme-editor
- Add theme-builder migration entry to housekeeping matrix
- Update legacy page counts from 137 to 138 in housekeeping tests
- Add /admin/theme-builder to content test prefixes

src/features/housekeeping/foundation/foundation-source-contract.test.ts

@@ -612,8 +612,8 @@ describe("housekeeping foundation completion contracts", () => {
 			HOUSEKEEPING_MIGRATION_MATRIX,
 		);
 
-		expect(HOUSEKEEPING_MIGRATION_MATRIX).toHaveLength(137);
-		expect(discovered).toHaveLength(137);
+		expect(HOUSEKEEPING_MIGRATION_MATRIX).toHaveLength(138);
+		expect(discovered).toHaveLength(138);
 		expect(issues).toEqual([]);
 	});
 });