refactor: establish Window folder feature - #339

Tracking issue: #342

Stack context

Part 29 of the Option 5 folder-feature stack.

• Previous: refactor: complete Device interface ownership #338
• Next: final helper cleanup and feature-graph guardrails

Review this PR as the incremental diff against #338.

Summary

• add the target src/window folder on the unqualified internal Window feature
• move Window, Document, browser globals, Location, XPath, CustomElementRegistry, and IdleDeadline out of the legacy DOM folder
• consolidate History and VisualViewport into the Window domain
• add the supported Window feature with its compiler-proven public dependencies
• remove the legacy qualified WebAPI.DOM source entry and the old standalone History/VisualViewport source features
• preserve every existing flat public module path

Dependency note

The provisional map listed only HTML. Existing Window, Document, and global signatures also expose Media, Storage, Messaging, Crypto, Performance, and ViewTransitions types. Those public domains are declared explicitly; HTML already supplies DOMNodes, Animation, CSSOM, Geometry, File, and foundational event/DOM layers.

Resolved temporary state

This PR removes the broad source feature named WebAPI.DOM. Supported qualified features can now expand through the top-level implication map without colliding with a legacy source entry; WebAPI.Window was verified directly.

Temporary state

• the mixed WebWorkersTypes cache/worker support module and BaseFile foundation coupling remain for final helper cleanup
• automated feature-graph guardrails remain deferred to the next PR, as requested, now that the complete folder stack exists

Review focus

• Window folder membership
• the expanded dependency closure
• removal of the legacy source-feature collision
• History and VisualViewport consolidation

Verification

• node_modules/.bin/rescript clean
• node_modules/.bin/rescript build --prod --features WebAPI.Window
• npm run build
• npm test
• npm run format:check
• git diff --check