Add a nanoFramework workload manifest packaging the SDK and templates

[danielmeza]

Description

The SDK design anticipates a nanoFramework workload manifest that packages the SDK together with the templates so a developer can install the whole nanoFramework toolchain with dotnet workload install nanoframework, rather than pinning the MSBuild SDK and the template package separately. The tooling spec lists this as component C11, explicitly scheduled for later. There is no tracking issue for it; this captures it so it is not lost.

How to solve the problem

Author a workload manifest that wraps the SDK and the dotnet new templates (and, optionally, the dotnet nano tool) into a single installable workload:

• Define the workload manifest and pack so dotnet workload install nanoframework provisions the SDK and templates at a coordinated version set.
• Decide the versioning/release relationship between the workload, the MSBuild SDK, and the templates.

This depends on the SDK being published (issue for CI/CD + publish) and the templates existing (the dotnet new templates issue).

Acceptance: dotnet workload install nanoframework installs the SDK and templates, after which dotnet new nanoapp + dotnet build works without separately pinning the MSBuild SDK or the template package.

Describe alternatives you've considered

• Keep pinning the MSBuild SDK (via global.json) and installing the template package separately. This is the current expectation and works; the workload is a convenience/onboarding improvement layered on top, hence its "later" scheduling.

Additional context

• Specification: 02 — SDK design §2.3 (option C) and 10 — tooling specs (component C11).
• Coverage and status: EXECUTION-PLAN.md — spec coverage matrix.
• Parent epic: SDK-style MSBuild project system for .NET nanoFramework #1784.
• Scope: later phase; depends on the published SDK and the templates.