refactor(app): remove legacy shell and onboarding layouts

[Foxpace]

Completes the phone View cleanup by removing shell, onboarding, preference, and landscape XML layouts.

What was added

• Removal of activity shell, app bar, navigation header, and content layouts.
• Removal of privacy, storage, battery, power-saver, and preference layouts.
• Removal of duplicated landscape variants and the API-specific preference screen.

How it works

The root Compose app now owns navigation and responsive layout. Composables adapt to available constraints and render onboarding and settings from state, so separate portrait, landscape, and API-version XML hierarchies are unnecessary.

Stack position

Layer 29 of 31 in the SensorBox refactor stack. Review this PR against its configured base to see only this layer.

Validation

• Full stack: ./gradlew test — BUILD SUCCESSFUL (160 tasks)

[Foxpace]

Superseded by #46, which targets master and shows the final current tree. Closing this stacked layer so review stays on the consolidated diff; this PR remains available as history.

[Foxpace]

Stack restored at the author's request. This PR is again part of the original 31-layer refactor chain. The architecture work continues as stacked PRs #47 through #54; consolidated PR #46 is superseded.