Add Assessment-driven page wave scripts

[TaoziZ03]

Summary

• Add an Assessment-driven script that transforms every approved representative Wiki/Web Part page.
• Add a second script that expands to all user-specified pages only after every representative page is validated as passed.
• Support interactive, device-login, certificate-thumbprint, and certificate-file authentication.
• Share source validation, transformation, logging, and result persistence through one common implementation.
• Add inline comments for each safety phase and a repeatable Pester test suite.

Companion documentation PR: SharePoint/sp-dev-docs#10964

Representative-page flow

Convert-RepresentativePages.ps1:

• Requires at least one Selected=true page for every IncludePattern=true pattern.
• Requires expected visible content and a validation owner.
• Supports -WhatIf, High-impact confirmation, and unattended certificate authentication.
• Creates draft pages without overwrite or source renaming.
• Writes each result immediately with ValidationStatus=Pending.

Wave expansion gate

Convert-SelectedPages.ps1 refuses to run unless:

• The original representative manifest and result set match one-to-one.
• Every result matches the current manifest SHA-256.
• Every representative has TransformationStatus=Created and ValidationStatus=Passed.
• The current PnP PowerShell version and Web Part mapping match the representative profile.
• Every additional page belongs to a pattern with a passed representative.

Safety

Both scripts:

• Require PowerShell 7.4.0 or later.
• Resolve the assessed list by GUID.
• Verify list URL, file URL, item parent list, and source modification time.
• Recheck the current web home page immediately before conversion.
• Bind ConvertTo-PnPPage by exact list item ID.
• Create drafts with -DontPublish.
• Don't use -Overwrite or -TakeSourcePageName.
• Persist every result row immediately and refuse result-file clobber without -Force.
• Cache connections and authentication failures.

The first version intentionally rejects:

• Publishing and Blog pages.
• Web-root pages and pages outside the default SitePages library.
• Home pages.
• Zero-part pages.
• Pages with item-level unique permissions.
• Unmapped pages without an explicit custom mapping file.

These cases require separately reviewed transformation paths.

Validation performed

• Pester: 7 passed, 0 failed.
• PowerShell AST parsing for all scripts.
• -WhatIf representative and expanded-wave runs against manifests derived from a 423-page Assessment.
• Mock full execution for both entry scripts.
• Interactive, certificate-thumbprint, and certificate-file branches.
• Result persistence and clobber protection.
• Representative validation, manifest hash, transformation profile, and unrepresented-pattern gates.
• Source modification, list identity, current-home-page, and unique-permission safety gates.

This PR is intentionally a draft for script-owner review.