Define the Application Builder template and sample matrix

## Objective

Select the minimum useful project and solution templates from the Epic proposal. Define which scenarios belong in shipping templates versus samples/docs, ensure C#/VB parity where applicable, and specify generated-file ownership, optional features, package references, and upgrade expectations.

## Completion guidance

- Keep the implementation focused on the objective while allowing the assignee to improve the approach based on research.
- Document important decisions, rejected alternatives, dependencies, and follow-up work.
- Add or update tests and documentation appropriate to the work.
- Verify locally and in CI where the task changes code or generated artifacts.

Start by locating and reviewing the referenced Epic proposal, then map its scenarios into shipping templates versus samples/docs. Define the template matrix, language parity, generated-file ownership, optional features, package references, and upgrade expectations; document decisions, rejected alternatives, dependencies, and follow-up work, with appropriate tests and documentation.

Written by the indexing model from the issue text.