Tracking issue: #342

Stack context

Part 28 of the Option 5 folder-feature stack.

• Previous: refactor: complete Canvas interface ownership #337
• Next: establish the Window folder and remove the legacy DOM source entry

Review this PR as the incremental diff against #337.

Summary

• move ScreenOrientation from the legacy DOM folder into src/device
• expose the existing flat module through WebAPI.Device
• leave the Device feature dependency closure unchanged

Why this follows the Device PR

The initial Device consolidation focused on the existing capability folders. ScreenOrientation was still published from the broad DOM folder even though it is an event-capable device/display interface. This one-file follow-up makes its ownership explicit before the Window layer removes the legacy folder.

Temporary state

• only Window/browser-entry interfaces remain in the legacy DOM folder
• the legacy broad WebAPI.DOM source entry is removed by the immediately following Window PR
• final feature-graph guardrails and helper cleanup remain deferred until the stack is complete

Review focus

• ScreenOrientation ownership
• unchanged flat public module path and Device closure

Verification

• node_modules/.bin/rescript clean
• node_modules/.bin/rescript build --prod --features DOM,Event,Device
• npm run build
• npm test
• npm run format:check
• git diff --check