[Task]: Support extending Platform API via a Plugin Development Kit (PDK)

Please select the area the issue is related to

Platform API

Please select the aspect the issue is related to

Aspect/API (API backends, definitions, contracts, interfaces, OpenAPI)

Description

Problem

platform-api can only be extended by editing it. A separate module cannot add its own REST APIs, config, or middleware without forking or patching platform-api sources.

Requirement

Make platform-api an importable library with a public, stable extension contract (a Plugin Development Kit), so a wrapper module can run and extend the full platform server by importing it — without changing platform-api.

At a high level:

• A wrapper can run the platform server and register its own plugins.
• A plugin can add REST APIs, an OpenAPI spec, and request-chain middleware.
• Plugins reach the platform through a public capability contract, never internal packages.
• Extension routes run under the platform's existing auth and scope enforcement.
• Extension is compile-time (by import); no runtime plugin loading.
• The default build behaves exactly as before.

Related:
N/A

No files, tests, or entry points are named. Start by locating the platform-api server entry point and its existing API, OpenAPI, authentication, scope-enforcement, and middleware boundaries. Done means a wrapper can import and run the server, plugins can register APIs, an OpenAPI spec, and middleware through a public contract, and the default build remains unchanged.