chore(web): add focused wallet element dev fixture

[rsomlette]

Review purpose

Add only the local development entry needed to load and inspect the accelerated-checkout element introduced in the preceding shell PR.

Stacked on wallets/release-01-component-shell.

Changes

• add a focused sample/wallets.html fixture
• resolve the public @shopify/checkout-kit/wallets package subpath in the sample
• build the sample as a separate Vite HTML entry
• add proxy-aware shop.dev local server configuration

Non-goals

• production wallet behavior
• a full wallet playground or cart builder
• Storefront API credentials or cart creation
• Portable Wallets loading
• public merchant contract decisions

Related ticket

Related: https://github.com/shop/issues-checkout/issues/14751

This provides the local fixture portion of the ticket. The fake adapter and lifecycle scenarios arrive in a later stacked PR, so this PR does not close the ticket.

Validation

• web lint and typecheck
• production package build
• multi-page sample build
• publint
• package snapshot comparison