refactor(payment): code standards fixes and regression repairs

Backend:
- Split payment_order.go (546→314 lines) into payment_order_lifecycle.go
- Replace magic strings with constants in factory, easypay, webhook handler
- Add rate limit/validity unit constants in payment_order_lifecycle, payment_service
- Fix critical regression: add PaymentEnabled to GetPublicSettings response
- Add missing migration 099_fix_migrated_purchase_menu_label_icon.sql

Frontend:
- Fix StripePopupView.vue: replace `as any` with typed interface, use extractApiErrorMessage
- Fix AdminOrderTable.vue: replace hardcoded column labels with i18n t() calls
- Fix SubscriptionsView.vue: replace hardcoded Today/Tomorrow with i18n
- Extract duplicate statusBadgeClass/canRefund/formatOrderDateTime to orderUtils.ts
- Add missing i18n keys: common.today, common.tomorrow, payment.orders.orderType/actions
- Remove dead PurchaseSubscriptionView.vue (replaced by PaymentView)

backend/migrations/099_fix_migrated_purchase_menu_label_icon.sql

@@ -0,0 +1,51 @@
+-- 097_fix_migrated_purchase_menu_label_icon.sql
+--
+-- Fixes the custom menu item created by migration 096: updates the label
+-- from hardcoded English "Purchase" to "充值/订阅", and sets the icon_svg
+-- to a credit-card SVG matching the sidebar CreditCardIcon.
+--
+-- Idempotent: only modifies items where id = 'migrated_purchase_subscription'.
+
+DO $$
+DECLARE
+    v_raw   text;
+    v_items jsonb;
+    v_idx   int;
+    v_icon  text;
+    v_elem  jsonb;
+    v_i     int := 0;
+BEGIN
+    SELECT value INTO v_raw
+      FROM settings WHERE key = 'custom_menu_items';
+
+    IF COALESCE(v_raw, '') = '' OR v_raw = 'null' THEN
+        RETURN;
+    END IF;
+
+    v_items := v_raw::jsonb;
+
+    -- Find the index of the migrated item by iterating the array
+    v_idx := NULL;
+    FOR v_elem IN SELECT jsonb_array_elements(v_items) LOOP
+        IF v_elem ->> 'id' = 'migrated_purchase_subscription' THEN
+            v_idx := v_i;
+            EXIT;
+        END IF;
+        v_i := v_i + 1;
+    END LOOP;
+
+    IF v_idx IS NULL THEN
+        RETURN;  -- item not found, nothing to fix
+    END IF;
+
+    -- Credit card SVG (Heroicons outline, matches CreditCardIcon in AppSidebar)
+    v_icon := '<svg fill="none" viewBox="0 0 24 24" stroke="currentColor" stroke-width="1.5"><path stroke-linecap="round" stroke-linejoin="round" d="M2.25 8.25h19.5M2.25 9h19.5m-16.5 5.25h6m-6 2.25h3m-3.75 3h15a2.25 2.25 0 002.25-2.25V6.75A2.25 2.25 0 0019.5 4.5h-15a2.25 2.25 0 00-2.25 2.25v10.5A2.25 2.25 0 004.5 19.5z"/></svg>';
+
+    -- Update label and icon_svg
+    v_items := jsonb_set(v_items, ARRAY[v_idx::text, 'label'],    '"充值/订阅"'::jsonb);
+    v_items := jsonb_set(v_items, ARRAY[v_idx::text, 'icon_svg'], to_jsonb(v_icon));
+
+    UPDATE settings SET value = v_items::text WHERE key = 'custom_menu_items';
+
+    RAISE NOTICE '[migration-097] Fixed migrated_purchase_subscription: label=充值/订阅, icon=CreditCard SVG';
+END $$;