Infrastructure: implement Azure Blob Storage adapter

Goal

Provide the first real, concrete implementation of the storage ports using the official Azure SDK.

Why

This is where the app actually talks to Azure (or Azurite in tests) for the first time.

Tasks

• Add the Azure.Storage.Blobs NuGet package to AzStorage.Infrastructure.
• Implement IStorageAccountConnector using BlobServiceClient, supporting all credential kinds modeled in the Domain storage-account issue (connection string, account key, SAS, Azure AD via DefaultAzureCredential/ClientSecretCredential).
• Map Azure SDK exceptions (RequestFailedException, etc.) to the domain-friendly failure reasons defined in the connection-abstraction issue.
• Add integration tests (using the Azurite setup) that connect successfully and that surface clear failures for wrong credentials/unreachable endpoint.

Acceptance Criteria

• Connecting to Azurite with a valid connection string succeeds end-to-end through the use case.
• Connecting with invalid credentials returns a mapped, specific failure — not a raw SDK exception bubbling up.

Depends on

• Application: storage account connection abstraction & use case
• Set up Azurite-based testing infrastructure for integration tests

Start in the AzStorage.Infrastructure project by locating IStorageAccountConnector and the storage-account connection use case, then review the Domain failure reasons and the Azurite testing setup. Add the Azure.Storage.Blobs-backed adapter and integration tests for valid connections, invalid credentials, and unreachable endpoints. Done means valid Azurite connections succeed through the use case and SDK failures become specific domain failures.