Complete control gallery and correct README examples

[HadenSmith]

Summary

The README startup example used undefined host types, and the undo example omitted its backing field and required base-class context. Replace them with an API-checked startup helper and a complete property fragment, explain WPF startup/resource requirements, and clarify theme persistence and undo recording. Correct the PowerShell fence and the Visual Studio prerequisite for .NET 10.

This also brings in the existing control-gallery commit: 18 demo screenshots, updated gallery captions and capture notes, and a synthetic CSV sample. No production code, package dependencies, or workflows change. Corrections to the remaining documentation are deferred.

Validation

• Reviewed all five README fenced snippets and inline API references against framework source; independent review found no blocking issues.
• Extracted and compiled all three C# snippets against the validated 1.0.5 packages: zero warnings/errors. Before correction, the undefined host types and missing backing field failed compilation.
• STA runtime checks passed for startup theme initialization before controller-factory invocation, runtime theme switching, and property notification/dirty-state/undo/redo behavior. The startup helper was compiled; these checks did not show a real shell window.
• dotnet build WPF-Framework.sln: zero warnings/errors.
• dotnet test WPF-Framework.sln: 7,038 passed, zero failed, six existing explicit OxyPlot skips (three unsupported/unimplemented deflate cases, two unsupported/unimplemented PDF cases, and one visible-window/STA test).
• scripts/test-release-artifact-contract.ps1: all 89 checks passed; no publication performed.
• Validated the pack command syntax/parameters, all local README links, all 22 gallery image links, image dimensions, and screenshot/caption agreement. git diff --check passed.

Release metadata

Audited central and assembly versions, all four package projects/nuspec release notes, pack-script expectations, dependency constraints, citation/codemeta metadata, and installation examples. They are consistent with the prepared 1.0.5 release; no metadata changes are needed. The existing v1.0.5 tag and its validated package artifacts remain unchanged by this documentation PR.