Add Stub_ShowProjectInbox to surface project items without Status

[Copilot]

This PR adds a new inbox stub to show project items that do not have a Status value, following the same implementation/test pattern used for existing project-item stubs. It also adds a focused test that reuses existing mock/test helper infrastructure.

• Problem addressed

  • Introduce a dedicated stub for “inbox” items (items with missing/empty Status) and cover it with tests using the current test module helpers/patterns.

• Production changes

  • Added Stub_ShowProjectInbox in public/items/project_item.ps1.
  • Behavior:
    • resolves project context (Owner/ProjectNumber)
    • retrieves items through Search-ProjectItem -IncludeDone -PassThru
    • filters to items where Status is null/empty/whitespace
    • returns raw items with -PassThru, otherwise pipes to Use-Order for interactive display

• Test changes

  • Added Test_StubShowProjectInbox_SUCCESS in Test/public/project_item.searchprojectitem.test.ps1.
  • Reuses existing mock project setup (Get-Mock_Project_700, MockCall_GetProject_700) and validates:
    • only empty-status items are returned
    • returned IDs match expected inbox candidates from mock data

function Stub_ShowProjectInbox{
    param([string]$Owner, [string]$ProjectNumber, [switch]$PassThru)

    ($Owner, $ProjectNumber) = Resolve-ProjectParameters -Owner $Owner -ProjectNumber $ProjectNumber
    $items = Search-ProjectItem -Owner $Owner -ProjectNumber $ProjectNumber -IncludeDone -PassThru
    $items = @($items | Where-Object { [string]::IsNullOrWhiteSpace($_.Status) })

    if($PassThru){ return $items }
    return $items | Use-Order
}