Refactor: Improve flight search UI and logic

This commit introduces several enhancements to the flight search user interface and underlying logic.

Key changes:
- Added an extension function `Flight.hasFlights()` to check if a flight object contains any actual flight data. This is located in `ui/home/src/main/kotlin/dev/adriankuta/flights/ui/home/extensions/FlightExt.kt`.
- In `StationsScreen.kt`:
    - The origin airport display now includes a "Origin airport" label.
    - The search input field placeholder text dynamically changes based on whether an origin airport has been selected (e.g., "Search origin airport" vs. "Search destination airport").
- In `StationsScreenViewModel.kt`:
    - When an airport is selected, the search query is now automatically cleared.
- Added new string resources in `ui/stations/src/main/res/values/strings.xml` for the dynamic placeholder text: `search_origin_airport` and `search_destination_airport`.
- In `SearchResults.kt`:
    - Implemented an `EmptyListComponent` to display a user-friendly message with an icon when no flights are found for the given search criteria.
    - The `SearchResults` composable now utilizes `itemsIndexed` for better handling of dividers between trip cards.
    - Dividers are no longer shown after the last item in the list of trips or trip dates.
    - Added previews for the empty list state (`EmptyListPreview` and `SearchResultsEmptyPreview`).

ui/stations/src/main/kotlin/dev/adriankuta/flights/ui/home/StationsScreen.kt

@@ -71,9 +71,21 @@ private fun StationsScreen(
             LaunchedEffect(selectedOriginAirport) {
                 selectedOriginAirport?.let { airportInfo = it }
             }
-            AirportInfoCompact(
-                data = airportInfo,
-            )
+            Column {
+                Text(
+                    text = "Origin airport",
+                    modifier = Modifier.padding(horizontal = 16.dp),
+                )
+                AirportInfoCompact(
+                    data = airportInfo,
+                )
+            }
+        }
+
+        val hintRes = if (selectedOriginAirport == null) {
+            R.string.search_origin_airport
+        } else {
+            R.string.search_destination_airport
         }
 
         OutlinedTextField(
@@ -82,7 +94,7 @@ private fun StationsScreen(
             modifier = Modifier
                 .fillMaxWidth()
                 .padding(16.dp),
-            placeholder = { Text(text = stringResource(R.string.search_airports)) },
+            placeholder = { Text(text = stringResource(hintRes)) },
             leadingIcon = { Icon(Icons.Default.Search, contentDescription = null) },
             singleLine = true,
         )

ui/stations/src/main/kotlin/dev/adriankuta/flights/ui/home/StationsScreenViewModel.kt

@@ -45,6 +45,7 @@ internal class StationsScreenViewModel @Inject constructor(
 
     fun onAirportSelected(airport: AirportInfo) {
         _selectedOriginAirport.value = airport
+        _searchQuery.value = ""
     }
 
     fun clearSelectedAirport() {

ui/stations/src/main/res/values/strings.xml

@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
     <string name="stations_screen_title">Stations</string>
-    <string name="search_airports">Search airports</string>
+    <string name="search_origin_airport">Search origin airport</string>
+    <string name="search_destination_airport">Search destination airport</string>
 </resources>