feat: Add passenger counter to home screen

This commit introduces a passenger counter component to the home screen, allowing users to specify the number of adults, teens, and children for their flight search.

Key changes:
- Added `ui:sharedui` module dependency to `ui:home`.
- Updated `PreviewDevices` annotation to include `showBackground = true`.
- Modified `HomeScreen`:
    - Added parameters to `HomeContent` and `SearchForm` for passenger count change callbacks.
    - Integrated the `Counter` composable from `ui:sharedui` for adults, teens, and children.
    - Added `VerticalDivider` between counters.
    - Updated previews to reflect passenger counter integration.
- Updated `HomeScreenViewModel`:
    - Introduced `MutableStateFlow` for `adultCount`, `teenCount`, and `childCount`.
    - Created `passengersState` flow by combining individual passenger count flows.
    - Updated `homeUiState` to include `passengersState`.
    - Added public functions `updateAdultCount`, `updateTeenCount`, and `updateChildCount` to modify passenger counts with validation.
    - Added `PassengersState` data class to hold passenger counts.
- Updated `Counter` composable in `ui:sharedui`:
    - Added an optional `minVal` parameter (defaulting to 0) to define the minimum allowed value for the counter.
    - Ensured the decrement button is disabled when the counter value reaches `minVal`.
    - Centered text in increment and decrement buttons.

ui/sharedui/src/main/kotlin/dev/adriankuta/flights/ui/sharedui/Counter.kt

@@ -37,6 +37,7 @@ fun Counter(
     onCountChange: (diff: Int) -> Unit,
     modifier: Modifier = Modifier,
     label: String? = null,
+    minVal: Int = 0,
 ) {
     val view = LocalView.current
 
@@ -86,11 +87,12 @@ fun Counter(
                     onCountChange(-1)
                 },
                 shape = MaterialTheme.shapes.medium,
-                enabled = value > 0,
+                enabled = value > minVal,
             ) {
                 Text(
                     text = "-",
                     style = MaterialTheme.typography.labelLarge,
+                    textAlign = TextAlign.Center,
                 )
             }
             Button(
@@ -105,6 +107,7 @@ fun Counter(
                 Text(
                     text = "+",
                     style = MaterialTheme.typography.labelLarge,
+                    textAlign = TextAlign.Center,
                 )
             }
         }