feat: implement WooCommerce AJAX product filtering

shop/docs/TESTING.md

@@ -63,6 +63,19 @@
 | RTL/LTR/dark/mobile: logical `woo.css` search dropdown (`fixed @640`), dark tokens, no overflow | ✅ Pass |
 | No `console.log` / `php -l` clean / `debug.log` clean | ✅ Pass |
 
+### M4 Gate (AJAX Filter) — manual QA 2026-09-13 (WP 7.1 / WC 11.1.0)
+
+| Check | Result |
+|-------|--------|
+| `GET /wp-json/xshop/v1/products?per_page=12` no filter → 4 items | ✅ Pass |
+| `category=uncategorized` →4, `min_price 100k max 200k` →1, `stock instock 3` `outofstock 1`, `on_sale 1` →1, `rating 4` →0, `orderby price_asc/desc` → sorted, `page 2 per_page 2` →2, `search Test`+category+sale →1, `min>max`→400, no private data | ✅ Pass |
+| UI: `product-filters.php` `data-xshop-filters` `chips` `price debounce` `sale/stock/rating` `orderby` `Apply/Clear` `drawer dialog` `aria-modal` | ✅ Pass |
+| JS: `filter.js` URL sync `history.pushState` `popstate` back/forward, `AbortController` stale `seq`, `debounce 300` price, `click outside` `Escape` focus trap, `aria-busy` `aria-live` | ✅ Pass |
+| No-JS fallback `GET /shop/?stock=instock` → server `xshop-products` **PASS**, `?on_sale=1` **PASS** | ✅ Pass |
+| Browser E2E (Playwright): category→ chips → remove → clear, sale→ grid, price, stock, sorting, pagination, rapid, back/forward, drawer open/close, search+filter coexist, no duplicate, no stale, no overflow 360/390/768/1024/1280 | ✅ Pass (duplicate form fixed) |
+| RTL `fa_IR` `dir=rtl` `xshop--rtl` + dark `data-theme` + mobile 390 drawer | ✅ Pass |
+| No `console.log` / `php -l` `filter.js` / `debug.log` clean | ✅ Pass |
+
 ## 3. Browser
 
 Chromium, Firefox, Edge, Safari (where available). Responsive: 360/768/1024/1280.