[P2] :core:designsystem: Material 3 theme and base components

[amaury901130]

AppTheme (color, typography, shape tokens, light/dark), AppButton, AppTextField with error state, AppTopBar, LoadingOverlay, ErrorDialog, AnnotatedString link helpers replacing TextView span extensions.

Acceptance criteria

• Components have previews (light/dark, sizes)
• No XML styles needed for UI

Reference: Android Base — Modernization Audit & Recommendations — section: Jetpack Compose migration