MCP Bundle (.mcpb): expose cloud (and tenant) as configurable user_config fields for sovereign cloud support

## Problem

The Azure MCP Server `.mcpb` bundle for Claude Desktop does not expose cloud or tenant configuration after installation. It therefore starts with the public-cloud defaults, even when the user needs Azure US Government or Azure China.

Other Azure MCP Server distributions support cloud selection through the `--cloud` launch argument or `AZURE_CLOUD`. Tenant selection is available through `AZURE_TENANT_ID`, but the MCP Bundle manifest does not expose either value in Claude Desktop's Extensions UI.

## Expected behavior

The Azure MCP Bundle manifest exposes non-sensitive `user_config` fields for the Azure cloud and tenant, then passes those values to the server using its supported configuration inputs.

## Acceptance criteria

- [ ] Claude Desktop's Extensions UI exposes an Azure cloud setting for the bundle.
- [ ] The cloud setting supports the documented values `AzureCloud`, `AzureChinaCloud`, and `AzureUSGovernment`, and preserves Azure public cloud as the default.
- [ ] Claude Desktop's Extensions UI exposes an optional Azure tenant ID setting.
- [ ] The configured values are passed to the server as `AZURE_CLOUD` and `AZURE_TENANT_ID` when the bundle starts.
- [ ] Leaving the tenant setting unset preserves the existing credential-chain behavior.
- [ ] The packed bundle passes MCPB manifest validation, and the sovereign-cloud documentation describes the bundle configuration path.