Organize source and add Todo sample

[MikeChristensen]

Summary

• organize the framework and unit tests under src/Imp and src/Imp.Tests
• preserve source history through Git-detected renames
• add a complete ASP.NET Core To Do sample with embedded templates, reusable layouts, dependency injection, query binding, postbacks, antiforgery protection, loops, dynamic routes, lifecycle hooks, CDN-aware assets, and custom error handling
• add sample application tests and include all projects in the solution and CI build
• update repository documentation, packaging paths, and workflows for the new layout
• avoid synchronous response-writer disposal so compiled templates render correctly under modern Kestrel without enabling synchronous I/O

Validation

• dotnet restore Imp.slnx
• dotnet build Imp.slnx --configuration Release --no-restore
• dotnet test Imp.slnx --configuration Release --no-build --no-restore (10 passed)
• dotnet pack src/Imp/Imp.csproj --configuration Release --no-build
• end-to-end HTTP smoke test of task creation, antiforgery validation, query filtering, dynamic task details, direct rendering, static assets, lifecycle headers, and custom 404 behavior
• git diff --check

Release note

The response-writer compatibility fix changes the published Imp runtime and should be released as a patch version after merge. Recommended next tag: v0.1.1.

No GitHub issue is associated with this work.