refactor(app): remove legacy onboarding and permissions

[Foxpace]

Removes the legacy onboarding and permission UI after the Compose replacement is wired.

What was added

• Removal of introduction, storage-folder, privacy-policy, and power-saver fragments.
• Removal of custom permission handler and settings dialog classes.

How it works

The Compose onboarding flow reads requirement state from MainViewModel and launches platform permission or settings requests through typed effects. Completion is persisted through AppPreferences, eliminating fragment-specific permission callbacks and navigation.

Stack position

Layer 25 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Superseded by #46, which targets master and shows the final current tree.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 The architecture work continues as stacked PRs #47 through #54; consolidated PR #46 is superseded.