fix(analytics): always render <Analytics.ProductView> on PDP

[paul-phan]

What

Remove the {selectedVariant && ...} guard around <Analytics.ProductView> in app/routes/products/product.tsx. The component now mounts on every PDP render.

Why

For combined-listing products (where the variant is resolved after hydration via useOptimisticVariant), selectedVariant is null on the first render. The truthiness guard skips the mount entirely, so:

• AnalyticsEvent.PRODUCT_VIEWED never dispatches
• view_item never reaches window.dataLayer
• GA4 e-comm tags wired to view_item never fire on combined-listing PDPs
• Hydrogen's <ShopifyAnalytics> is missing the product context for downstream events on the same visit

The fallback values selectedVariant?.price.amount || "0", selectedVariant?.id || "", selectedVariant?.title || "" were already in place inside the JSX — they just weren't reachable behind the guard. Removing the guard activates them as intended.

Behaviour change

• Before: view_item fires only after selectedVariant resolves (which is post-hydration for combined listings — often after the user has already interacted with the page).
• After: view_item fires on first render for every product, with safe fallback values when variant data isn't loaded yet.

For products where selectedVariant IS available on first render (the majority — standard non-combined products), behaviour is unchanged.

Verification

1. Open any PDP, especially a combined-listing product.
2. Check the GA4 DebugView or GTM Preview — view_item should appear on initial page load.
3. Confirm price/variant fields populate correctly once selectedVariant resolves (they're reactive bindings, so the analytics payload updates if needed for subsequent events).

Risk

Minimal. The change reverses a defensive guard that was over-restrictive; the fallback values handle the no-variant case gracefully. Tested locally on standard products, combined listings, and bundled products.