[IMP] website_sale_aplicoop: filter and cap stock using forecasted net qty

Group orders are not confirmed until the cutoff date, so draft/sent
sale.order lines never generate stock.moves and are invisible to
virtual_available. This change makes the shop aware of that demand.

- group.order._compute_draft_sale_demand: queries sale.order.line in
  draft/sent state (mirroring sale_stock forecasted report logic) and
  returns pending demand per product.id in the product's own UoM.
- _get_products_for_group_order: delegates to new _apply_stock_filter_and_sort
  which excludes storable products whose forecasted net qty
  (virtual_available − draft demand) <= 0, unless allow_out_of_stock_order.
- _compute_stock_ribbons: reads draft_demand_by_product from ORM context
  so is_out_of_stock / is_low_stock / dynamic_ribbon_id reflect net qty.
- Controller: new _prepare_draft_stock_data helper calculates demand once
  per request, injects context, and builds product_max_qty dict. Applied
  in eskaera_shop, load_eskaera_page and load_products_ajax.
- Template: qty input gets max and data-max-qty from product_max_qty.
- JS: blocks add-to-cart if requested quantity exceeds data-max-qty.
- Fixes type check: type=='consu' → is_storable=True (Odoo 18 semantics).
- 21 new tests in test_forecasted_stock.py covering demand calculation,
  ribbon logic with context, and group order filtering.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

website_sale_aplicoop/views/website_templates.xml

@@ -720,7 +720,7 @@
                                 <button class="qty-decrease" type="button" t-attf-data-product-id="{{ product.id }}" aria-label="Decrease quantity">
                                     <i class="fa fa-minus" />
                                 </button>
-                                <input type="number" t-attf-id="qty_{{ product.id }}" class="product-qty" name="quantity" t-attf-value="1" t-attf-min="{{ quantity_step }}" t-attf-step="{{ quantity_step }}" />
+                                <input type="number" t-attf-id="qty_{{ product.id }}" class="product-qty" name="quantity" t-attf-value="1" t-attf-min="{{ quantity_step }}" t-attf-step="{{ quantity_step }}" t-att-max="product_max_qty.get(product.id) if product_max_qty else None" t-att-data-max-qty="product_max_qty.get(product.id) if product_max_qty else None" />
                                 <button class="qty-increase" type="button" t-attf-data-product-id="{{ product.id }}" aria-label="Increase quantity">
                                     <i class="fa fa-plus" />
                                 </button>