[Performance] Update Store UI asset references to use fingerprinted URLs via @Assets[...]

[VancouverBen]

Summary

Adopt the Blazor-recommended asset referencing pattern for .NET 9+ (@Assets["..."]) in the Store Blazor Server app for CSS/JS (and any other static assets referenced from components/layouts).

Why

With MapStaticAssets, ASP.NET Core fingerprints assets and sets caching headers (including immutable) so browsers cache assets indefinitely until content changes. Using @Assets["..."] ensures the app emits the correct fingerprinted URL.

Guidance (docs)

• Blazor static files (ComponentBase.Assets / @Assets[...]): https://learn.microsoft.com/aspnet/core/blazor/fundamentals/static-files?view=aspnetcore-10.0
• Static files in ASP.NET Core (fingerprinting, caching): https://learn.microsoft.com/aspnet/core/fundamentals/static-files?view=aspnetcore-10.0

Acceptance criteria

• CSS/JS references in root components/layouts use @Assets["{PATH}"] where applicable.
• No regressions in styling or script loading.
• Validate that ImagePrefix guidance remains intact for product images (do not break existing ImagePrefix usage).