Add assembly-to-package mappings for ProxyGenerator

[Copilot]

Types from referenced assemblies that have a corresponding npm package should be imported from that package rather than generated as local TypeScript files. This adds a configurable mapping from C# assembly name to npm package name.

Added

• AssemblyToPackageMapping MSBuild ItemGroup support — maps C# assembly types to an npm package instead of generating local TypeScript files

<ItemGroup>
    <AssemblyToPackageMapping Assembly="MyCompany.Shared" Package="@mycompany/shared" />
</ItemGroup>

• --assembly-to-package=Assembly=Package CLI flag (repeatable) for direct proxy generator invocation
• TypeExtensions.SetAssemblyPackageMappings() / IsFromMappedAssembly() for configuring and querying the mapping at runtime
• Specs covering GetTargetType, IsFromMappedAssembly, CollectTypesInvolved exclusion, and an end-to-end command generation scenario
• Documentation for the new feature in configuration.md with a relatable multi-project shared library example

Changed

• Generator.Generate() accepts an optional assemblyPackageMappings dictionary and filters mapped types from generated typeDescriptors / enumDescriptors
• GetTargetType() returns a package-based TargetType (FromPackage=true, Module=<packageName>) for types whose assembly is mapped
• All CollectTypesInvolved overloads skip types from mapped assemblies to prevent recursive local type generation

[einari]

@copilot Great. I had an error in the spec; AssemblyToPageMapping should be AssemblyToPackageMapping. Let's create a better sample than the Cratis sample in the documentation, something others can relate to - like a reusable .NET Project that gets used by multiple other projects.

[Copilot]

@copilot Great. I had an error in the spec; AssemblyToPageMapping should be AssemblyToPackageMapping. Let's create a better sample than the Cratis sample in the documentation, something others can rel...

The AssemblyToPageMapping typo was already fixed in a previous commit. I've now also rewritten the documentation example (4d00147) to use a generic multi-project solution structure (MyCompany.Shared / MyCompany.Inventory / MyCompany.Purchasing) with a shared class library that ships both a NuGet package and an npm package — a pattern most .NET teams will recognise.

[einari]

@copilot fix the markdown lint errors - run the verification script in the Documentation folder

[github-actions]

NuGet packages for this PR, e.g. Cratis.Arc:
https://github.com/cratis/arc/packages/1655206?version=20.13.1-pr2189.03c1910

[Copilot]

@copilot fix the markdown lint errors - run the verification script in the Documentation folder

Fixed in 6c058c6 — the solution structure code block was missing a language specifier (text). All markdown checks now pass.

[einari]

Superseded by #2187 which now includes both the assembly-to-package mapping feature and the flags enum template support.