Add helix-shared-queue-sqs backend package (BatchedQueueClient successor)

## Why

Concrete SQS backend for the `helix-shared-queue` base package (#1269), intended as a successor to `BatchedQueueClient` (`@adobe/helix-admin-support`) that other services can adopt without depending on a hand-rolled local abstraction.

## Scope

- `QueueSqs extends Queue`, pre-wiring a `backendFactory` exactly like `StorageS3.fromContext`:
```js
export class QueueSqs extends Queue {
static fromContext(context, opts = {}) {
return super.fromContext(context, {
backendFactory: createDefaultBackendFactory(context.env, { log: context.log }),
...opts,
});
}
}
```
- `SqsQueueBackend` — behavior-preserving port of `BatchedQueueClient`:
- `sendBatch`: pack messages into ≤10-entry/≤256KB `SendMessageBatchCommand` batches (SQS API limits).
- Single-oversized-message spill to blob storage via an injected `Storage`/`Bucket` (see #1269) instead of a hardcoded `S3Client`.
- `receiveBatch`/`deleteBatch`: port of `BatchedQueueClient.receive()`/`delete()` long-poll + batch-delete.
- Drop `BatchedQueueClient`'s "whole batch failed -> store to S3 as undeliverable" fallback unless usage data shows it's actually relied upon; log + rethrow instead, consistent with how current call sites don't catch `.send()` errors.
- Queue naming/addressing (region/account-derived SQS URLs) is internal to this backend, not exposed to callers as a URL — callers pass a logical queue name.

## Acceptance

- Test suite mirrors `helix-shared-storage-s3`'s conventions, covering batching, spill, receive, delete against nock'd SQS endpoints.
- Consumers (e.g. helix-api-service) can adopt this via a one-line import swap (`import { Queue } from '@adobe/helix-shared-queue'` -> `import { QueueSqs as Queue } from '@adobe/helix-shared-queue-sqs'`), no call-site logic changes beyond that swap.

Depends on: #1269

Start with prerequisite issue #1269, then compare the existing BatchedQueueClient behavior with StorageS3.fromContext and helix-shared-storage-s3 test conventions. Done means a QueueSqs and SqsQueueBackend implementation covers batching, oversized-message spill, receive, and delete against nock'd SQS endpoints, with the documented one-line consumer import swap.

Written by the indexing model from the issue text.