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/migration/discover-legacy-pages.test.ts

@@ -29,7 +29,7 @@ describe("discoverLegacyPages", () => {
 	it("discovers the exact legacy administration inventory", () => {
 		const pages = discoverLegacyPages();
 
-		expect(pages).toHaveLength(137);
+		expect(pages).toHaveLength(138);
 		expect(pages).toContainEqual({
 			surface: "admin",
 			legacyPath: "/admin/users/:id/edit",