Simplify package module/type structure

Summary

Pre-alpha breaking cleanup to simplify the package structure and make the public surface more consistent.

This issue tracks the refactor to:

• rename root *API type-holder modules to *Types
• keep the existing folder structure for concrete modules
• export the primary concrete type as t
• selectively re-export additional public helper types from the concrete module that uses them
• remove unrelated open usage
• remove trivial primitive aliases like string, bool, unit, and low-value callback aliases where they do not add meaning
• remove window and navigator from Global without deleting Global
• shift access toward owner modules such as Window, Navigator, History, Storage, Performance, and similar modules
• avoid introducing any new include directives as part of the simplification

Out Of Scope

• contributor docs
• code-generation conventions
• deleting Global
• flattening the folder structure

Execution Order

• #239 must land first
• #238, #240, #241, and #243 can run in parallel after #239
• #242 is the final integration pass

Linked Issues

• #239 Shared groundwork for package simplification
• #238 Simplify DOM, event, and observer module surfaces
• #240 Simplify fetch, file, canvas, URL, and socket module surfaces
• #241 Move runtime capability access away from Global window and navigator
• #243 Simplify media and device module surfaces
• #242 Final integration for package simplification

Acceptance Criteria

• No root src/*API.res type-holder files remain; they are replaced by src/*Types.res.
• The existing folder structure remains in place.
• Each concrete module exports its main type as t.
• Concrete modules selectively re-export secondary public types only where justified.
• Unrelated open usage is removed.
• No new include directives are introduced by this refactor.
• Trivial primitive aliases are removed instead of being renamed or moved.
• Global.window and Global.navigator are removed.
• Source and tests stop depending on Global.window and Global.navigator.
• The package passes npm run build and npm test after integration.