[3.0] Delete the deprecated IntelliTect.CredentialManager module folder and tests

[MarkMichaelis]

Summary

IntelliTect.CredentialManager was hard-deprecated in IntelliTect.PSToolbox 2.1.0 (removed from the umbrella's RequiredModules; manifest tagged Deprecated; Write-Warning on import; full migration guide in Modules/IntelliTect.CredentialManager/DEPRECATED.md). The PSGallery package IntelliTect.CredentialManager 1.1.1.1 will be unlisted when #117 is resolved.

In IntelliTect.PSToolbox 3.0, the on-disk module should be deleted entirely. Tracking that here so we don't forget.

Deliverables

• Delete Modules/IntelliTect.CredentialManager/ (entire folder, including .psm1, .psd1, DEPRECATED.md)
• Delete Modules.Tests/CredentialManager.Tests.ps1 (all tests are already commented out)
• Remove any stragglers from PROJECT_OVERVIEW.md §2.4 and the §6 deprecation matrix
• Remove any remaining mentions of the module from README.md and CONTRIBUTING.md
• Verify the research report link in DEPRECATED.md either dies cleanly with the file or is preserved elsewhere
• Bump umbrella IntelliTect.PSToolbox to 3.0.0 in the release containing this change
• Release notes call out the deletion as a breaking change

Why a major bump

Anyone still doing Install-Module IntelliTect.PSToolbox and relying on Get-CredentialManagerCredential / Set-CredentialManagerCredential etc. via the umbrella will already get CommandNotFoundException after 2.1.0 (module removed from RequiredModules). The 3.0 deletion completes the lifecycle — direct Install-Module IntelliTect.CredentialManager will still work against PSGallery 1.1.1.1 until #117-driven unlist lands.

Depends on

• Cannot publish/unlist modules in PSGallery: MarkMichaelis is not an owner of any IntelliTect.* package #117 (to actually unlist the PSGallery package)
• A 3.0 release milestone existing

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com