Add OfficeIMO Word Excel and PowerPoint feature wave

[PrzemyslawKlys]

Summary

• add Word markdown conversion cmdlets and round-trip tests
• expand Excel with TOC/range readers, chart formatting, smart hyperlinks, URL image helpers, internal link helpers, and URL link helpers
• expand PowerPoint with sections, text replacement, slide import/copy, transitions, slide sizing, theme inspection/update cmdlets, and slide layout switching
• refresh README/OVERVIEW plus add docs and examples for the new surfaces

Testing

• dotnet build .\Sources\PSWriteOffice.sln -c Debug
• pwsh -NoLogo -NoProfile -Command "Invoke-Pester .\Tests\ExcelDsl.Tests.ps1 -Output Detailed"
• pwsh -NoLogo -NoProfile -Command "Invoke-Pester .\Tests\PowerPoint.Tests.ps1 -Output Detailed"
• pwsh -NoLogo -NoProfile -File .\PSWriteOffice.Tests.ps1 -SkipDependencyInstall

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