Performance: Delay WebGL model initialization until the 3D Viewer ent…

[pradeep0153]

Closes #380.

Description

This PR executes a highly critical performance optimization on the Product Display Page (PDP), resolving severe main-thread blocking and unacceptable Time to Interactive (TTI) metrics caused by the eager initialization of the WebGL 3D Viewer.

Changes Made

• Performance Profiling: Audited the PDP using Google Lighthouse and the Chrome Performance tab. Discovered that the <ThreeDViewer /> component was aggressively instantiating the Three.js WebGL context and executing synchronous downloads of massive 15MB+ .gltf 3D assets immediately upon page load, even if the viewer was located completely below the fold.
• Intersection Observer Architecture: Engineered a strict lazy-loading architecture utilizing the modern IntersectionObserver API (via react-intersection-observer).
• Static Fallback Rendering: The component now renders a lightweight, highly optimized, static AVIF image placeholder by default, ensuring a near-instantaneous initial render.
• Deferred Execution: The heavy Three.js engine, the WebGL canvas initialization, and the massive network requests for the 3D assets are now strictly deferred. They are only triggered the exact millisecond the user scrolls the placeholder image into the visual viewport (or explicitly taps a "View in 3D" action button).

Impact

• Core Web Vitals & Mobile UX: Forcing a mobile device on a 3G network to eagerly download and parse 15MB of 3D geometry before the user can even scroll down to read the product description completely destroys the user experience and severely penalizes SEO rankings. By deferring the WebGL initialization until it is actively required, we completely unblock the main JavaScript thread during the critical initial hydration phase. This mathematically guarantees lightning-fast TTI scores, skyrockets our Core Web Vitals, and ensures the page feels instantly responsive to every customer.

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