Enhancement: Add support for built-in Microsoft site designs (store 1) to spo sitedesign commands

Description

spo sitedesign apply, spo sitedesign get and spo sitedesign list only reach tenant-registered custom site designs (store 0) via the SiteScriptUtility REST API. Microsoft's built-in site designs (e.g. Event, Department, Human Resources) live in a separate store ("store 1") and can currently only be reached by adding "store": 1 to the same REST calls, or by falling back to a raw m365 request call — there's no first-class way to list, get or apply them through the CLI today.

Proposal

• spo sitedesign list --builtIn — lists the built-in Microsoft site designs.
• spo sitedesign get --builtIn (--id|--title) — retrieves a single built-in design.
• spo sitedesign apply (--id --builtIn | --template <name>) — applies a built-in design, either by id or by a friendly template name (e.g. Event, Department, HumanResources).

Prior art

PnP PowerShell already implemented the equivalent behaviour for Get-PnPSiteDesign -BuiltIn and Invoke-PnPSiteDesign -Template: https://github.com/pnp/powershell/pull/5358

Start by examining the existing spo sitedesign apply, get, and list command entry points and their SiteScriptUtility REST calls. Compare the store 0 handling with the proposed store 1 behavior, then verify that built-in designs can be listed, retrieved by ID or title, and applied by ID or template name.