Polish UI + freshen core deps

- Rewrote MainScreen: top bar, prominent status hero (idle/clear/watching/alert), active vs trusted sections, per-tracker cards with status icons, and a detail bottom sheet with co-movement evidence + trust action.
- Sensitivity selector with per-mode explanation; on-device/no-network footer.
- core-ktx 1.13.1->1.15.0, activity-compose 1.9.3->1.10.1 (kept the proven Kotlin/AGP/Compose matrix for build stability).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0187UiEtasyowhEBYs6s9iF5

gradle/libs.versions.toml

@@ -2,9 +2,9 @@
 agp = "8.7.3"
 kotlin = "2.0.21"
 ksp = "2.0.21-1.0.28"
-coreKtx = "1.13.1"
+coreKtx = "1.15.0"
 lifecycle = "2.8.7"
-activityCompose = "1.9.3"
+activityCompose = "1.10.1"
 composeBom = "2024.12.01"
 material3 = "1.3.1"
 playServicesLocation = "21.3.0"