Inventory Visual Basic Application Framework behavior and define the parity contract

## Objective

Create an authoritative capability and compatibility matrix from the current VB Application Framework, implementation, documentation, and known issues. Include startup/shutdown, cancellation, unhandled exceptions, single instance, next-instance activation, command line, splash screen, application info, network availability, settings-on-exit, threading, and design-time/template behavior.

## 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 inventorying the current VB Application Framework implementation, documentation, and known issues across the listed behavior areas. Done means an authoritative capability and compatibility matrix exists, with decisions, rejected alternatives, dependencies, and follow-up work recorded; update relevant tests and documentation and verify locally or in CI where applicable.

Written by the indexing model from the issue text.