Typescript definitions support

## The problem to solve

When developing modules based on the self pattern we often don't see if a function really exists, where it is declared etc.

## Proposed solution

Add typescript definition file at root project and

## Alternatives

- rewrite apostrophe in typescript or other typed language that transpiles to javascript. This option would cost a lot with few benefits
- use jsdoc. This option is complicated because jsdoc does not handle all the type, however we can combine jsdoc and typescript definitions together.

## Additional context

I already started a POC with few definitions

The issue names no files, tests, or entry points; begin by locating the existing POC and reviewing the root project structure and public module APIs. Done means a root-level TypeScript definition file supports the relevant self-pattern modules and lets developers verify function existence and declarations, although the issue does not specify test coverage.

Written by the indexing model from the issue text.