fix(storefront): SD-10795 Out_of_Stock banner is duplicated and overlaps Add_to_cart button on PDP

[bc-yevhenii-buliuk]

What?

This PR fixes duplicate OOS banners and overlapping Add to Cart button on PDP.
Also it eliminates unnecessary AJAX on initial page load (addresses feedback from @bc-jz in PR #2198)

Additional info for visibility:
Problem:

• Duplicate OOS banners appearing on PDP (product-level banner from Handlebars + variant-level banner from JS).
• Unnecessary AJAX call on initial page load when product has default options.

Changes:

• Moved product-level OOS banner inside add-to-cart-wrapper component for correct layout positioning.
• Added duplicate banner prevention in showMessageBox to avoid showing variant-level banner if product-level banner already exists.
• Removed unnecessary AJAX call on initial load by using BCData.product_attributes from Stencil context, which now contains correct data after PR #46317.

Requirements

• CHANGELOG.md entry added (required for code changes only)

Tickets / Documentation

• SD-10795

Screenshots (if appropriate)

bug (track inventory on product level)

behavior after fix (track inventory on product level)

sd_10795_fix_inventory_on_product_level.mov

behavior after fix (track inventory on variant level)

sd_10795_fix_inventory_on_variant_level.mov.mov

unify out-of-stock banner styling for product and variant levels

[bc-alexsaiannyi]

looks good

[jkanive]

@bc-yevhenii-buliuk Do you know why we have 2 different color for Sold Out message box? Its different for product level and variant level if I am seeing it correctly. But its the same message. Maybe its intentional.

[bc-yevhenii-buliuk]

@bc-yevhenii-buliuk Do you know why we have 2 different color for Sold Out message box? Its different for product level and variant level if I am seeing it correctly. But its the same message. Maybe its intentional.

@jkanive As far as I know, it wasn't intentional - the variant-level banner was using a common alert style while product-level used error styling. I've unified them both to use error styling (red) for consistency.