Restore notifications bell once a backend notifications feed endpoint exists

[ahmetabdullahgultekin]

Why: The dashboard notifications bell is hidden because there is no backend notifications-feed endpoint yet (the screen was permanently 'No notifications yet'). Navigation remains wired; only the entry point is hidden.

Done when: a backend feed endpoint ships, the NotificationsScreen loads real data, and the bell is restored in the dashboard top bar.

source: androidApp/src/main/kotlin/com/fivucsas/mobile/android/ui/screen/DashboardScreen.kt:228

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Migrated from androidApp/src/main/kotlin/com/fivucsas/mobile/android/ui/screen/DashboardScreen.kt:228.