Application: upload, download and delete blob use cases

Goal

Implement the core file-transfer operations every storage browser needs.

Why

Upload/download/delete is the minimum viable "does something useful" slice of the app, and progress/cancellation support is something users frequently complain is clunky or missing in Storage Explorer.

Tasks

• Add ports for UploadBlobAsync, DownloadBlobAsync, DeleteBlobAsync (and container delete) in AzStorage.Application.
• Add use cases wrapping these operations, accepting an IProgress<long>-style callback and a CancellationToken so a future UI can show progress bars and let users cancel.
• Implement in AzStorage.Infrastructure using the Azure SDK's built-in transfer/progress APIs.
• Add integration tests (Azurite) covering: upload then download round-trip (content matches), delete removes the blob, cancellation actually stops an in-progress transfer.

Acceptance Criteria

• Round-trip upload/download test verifies byte-for-byte content equality.
• Cancelling an upload/download mid-transfer is verified by a test (e.g. using a CancellationTokenSource with a short delay).

Depends on

• Application: list containers & blobs with pagination

Start in the AzStorage.Application and AzStorage.Infrastructure projects, then review the Azure SDK transfer and progress APIs. Use Azurite integration tests as the starting point and cover upload/download byte equality, blob deletion, and cancellation during an in-progress transfer. The work is done when the listed ports, use cases, infrastructure implementations, and acceptance tests are complete.