feat(app): add Compose onboarding and about flows

[Foxpace]

Replaces the legacy introduction flow with Compose onboarding, privacy, and project information screens.

What was added

• Guided onboarding for privacy, storage, lifecycle, and battery requirements.
• A dedicated privacy-policy screen.
• An About screen for project and open-source information.

How it works

The onboarding screen advances through requirement-specific pages and emits intents when the user grants access or acknowledges a step. Completion is stored in preferences, allowing the root navigation state to enter the main application on subsequent launches.

Stack position

Layer 12 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Superseded by #46, which targets master and shows the final current tree.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 The architecture work continues as stacked PRs #47 through #54; consolidated PR #46 is superseded.