Resolve discount app intents after save or cancel

[iphipps]

Why

Follow-up to #75. The registered React Router discount intent links currently save or navigate without resolving the intent, leaving Sidekick or another invoker waiting for the declared output.

What changed

• return the authoritative discountId from create and update mutations
• resolve successful intent saves with shopify.intents.response.ok({id})
• resolve intent cancellation with shopify.intents.response.closed()
• preserve existing navigation when the page was not opened as an intent
• upgrade App Bridge types so the request and response APIs are typed
• add source tags for the associated shopify.dev tutorial

Validation

• pnpm exec tsc --noEmit
• targeted ESLint
• targeted Prettier
• env -u HOST -u SHOPIFY_APP_URL pnpm run build
• git diff --check

Dependency for shop/world#919168.

[iphipps]

@loic-d Could you review and merge this into the #75 branch? It addresses the valid Binks finding on shop/world#919168 and is required before the docs PR can land.