android: unify main tabs shell and hide bottom bar on scroll

android/CHANGELOG.md

@@ -474,3 +474,11 @@
   - attachment/media markers (`movie`, `attach file`).
 - Replaced chat list management FAB glyph toggle (`+`/`×`) with Material `Add`/`Close` icons.
 - Added `androidx.compose.material:material-icons-extended` dependency for consistent icon usage.
+
+### Step 76 - Shared main tabs shell with scroll-aware visibility
+- Moved `Chats / Contacts / Settings / Profile` bottom panel to a shared navigation shell (`AppNavGraph`) so it behaves as global page navigation.
+- Added dedicated `Contacts` page route and wired it into main tabs.
+- Removed local duplicated bottom panel from chat list screen.
+- Implemented scroll-direction behavior for all 4 main pages:
+  - hide panel on downward scroll,
+  - show panel on upward scroll / at top.