fix(e2e): dual-stack selector compatibility — 18/18 specs pass on Tauri

- selectors.ts: dual CSS selectors for all divergent class names
- actions.ts: fallback DOM queries (try primary, then alternatives)
- assertions.ts: waitUntil with dual selectors
- 12 spec files updated with graceful skip for stack-specific features
- 175 tests pass, 30 skip (expected: groups/diagnostics Tauri-absent)

tests/e2e/specs/theme.test.ts

@@ -87,7 +87,7 @@ describe('Theme system', () => {
     const count = await browser.execute(() => {
       const items = document.querySelectorAll('.dd-item, .dropdown-item');
       let catCount = 0;
-      const catNames = ['mocha', 'macchiato', 'frappe', 'latte'];
+      const catNames = ['mocha', 'macchiato', 'frapp', 'latte'];
       for (const item of items) {
         const text = (item.textContent ?? '').toLowerCase();
         if (catNames.some(n => text.includes(n))) catCount++;