[P1] Split into :core and :feature modules

[amaury901130]

Create :app, :feature:auth, :feature:profile, :core:domain, :core:data, :core:network, :core:datastore, :core:designsystem, :core:testing. Features must not depend on each other.

Acceptance criteria

• Modules exist and build
• No feature-to-feature dependencies

Reference: Android Base — Modernization Audit & Recommendations — section: Target architecture