Fix: removing a wishlisted item from the shop sidebar shows raw JSON

[sjfgzzwd9w-maker]

Summary

Fixes #252.

Clicking the × on an item in the shop page's WISHLIST sidebar widget
(app/components/discover_rail/shop_wishlist_widget.html.erb) submits a
button_to ... method: :delete form. Turbo Drive intercepts this and expects
an HTML/Turbo Stream response, but Shop::WishlistsController#destroy only
ever rendered render json: { wishlisted: false }. Turbo can't process a bare
JSON response, so it ends up displaying the raw {"wishlisted":false} JSON
instead of removing the item from the list.

Fix

• Shop::WishlistsController#destroy now responds to both formats:
  • format.json — unchanged, still returns { wishlisted: false } for the
    shop-wishlist Stimulus controller's fetch() calls (used by the star
    toggle on item cards).
  • format.turbo_stream — new, renders
    turbo_stream.remove("shop_wishlist_item_#{params[:id]}"), which is what
    the sidebar widget's button_to form now receives via Turbo Drive.
• discover_rail/shop_wishlist_widget.html.erb — added
  id="shop_wishlist_item_<%= item.id %>" to each .shop-goals__item so the
  turbo stream remove action has a target to remove.

This is a small, additive change (respond_to + one id attribute) and
doesn't touch the existing JSON path used elsewhere.

Testing

Ran the app locally via docker compose (Rails 8.1, dev env), signed in as
an existing user with an item wishlisted, and exercised the endpoint exactly
as the browser would.

Before (on main) — Turbo-driven DELETE returns raw JSON, which Turbo
shows as the page body:

{"wishlisted":false}

After (this branch) — same request now returns a turbo stream that
removes just that item:

$ curl -X DELETE /shop/wishlists/1 \
    -H "Accept: text/vnd.turbo-stream.html, text/html, application/xhtml+xml" \
    -H "X-CSRF-Token: ..."
status=200 content_type=text/vnd.turbo-stream.html; charset=utf-8

<turbo-stream action="remove" target="shop_wishlist_item_1"></turbo-stream>

• Confirmed the ShopWishlist row is deleted from the DB.
• Confirmed /shop falls back to the "Tap the star on any item to add it
  here." placeholder once the wishlist is empty.
• Confirmed the existing JSON path (item-card star toggle,
  Accept: application/json) is unaffected — still returns
  {"wishlisted":true} / {"wishlisted":false}.
• Probed double-removal and a non-existent item id — both return a clean
  200 turbo-stream no-op (no errors).

AI disclosure

This PR was implemented and verified by Claude Code (Anthropic): it
identified the root cause, wrote the fix, and ran the verification steps
above (boot the app via Docker, sign in, and exercise the endpoint) against
a local dev environment.