Add solution file covering all 37 sample projects

The previous "AI in .Net.sln" was generated with doubled paths
(code\generative-ai-dotnet-samples\samples\... inside a file already
located at code\generative-ai-dotnet-samples\), so every project
reference was broken. Regenerated from scratch via `dotnet new sln`
plus `dotnet sln add` over `find samples -name '*.csproj'`.

`dotnet build "AI in .Net.sln"` now succeeds for all 37 projects.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: NinjaRocks