Backdrop improvements (#476)

## Description

The backdrop image shown on most pages is now configurable in advanced
settings:
* Image w/ dynamic color - Shows the backdrop with dynamic color filling
the entire space (new default)
* Image only - Shows only the backdrop image (current Wholphin behavior)
* None - Don't show any backdrops

Additionally, the backdrop is retained between page loads for the same
items.

## Acknowledgements

Big thanks to @YogiBear12 from which the idea and implementation for the
dynamic color was adapted from!

Code adapted from
https://github.com/YogiBear12/Halfin/blob/main/COLOR_EXTRACTION_AND_BACKDROP.md#backdrop-fading-and-transitions

## Issues

Closes #221
Closes #461
Closes #442



https://github.com/user-attachments/assets/1acbc487-c697-44d7-89ed-e7e4c9169360

app/src/main/java/com/github/damontecres/wholphin/preferences/AppPreference.kt

@@ -659,6 +659,19 @@ sealed interface AppPreference<Pref, T> {
                 summaryOff = R.string.disabled,
             )
 
+        val BackdropStylePref =
+            AppChoicePreference<AppPreferences, BackdropStyle>(
+                title = R.string.backdrop_display,
+                defaultValue = BackdropStyle.BACKDROP_DYNAMIC_COLOR,
+                getter = { it.interfacePreferences.backdropStyle },
+                setter = { prefs, value ->
+                    prefs.updateInterfacePreferences { backdropStyle = value }
+                },
+                displayValues = R.array.backdrop_style_options,
+                indexToValue = { BackdropStyle.forNumber(it) },
+                valueToIndex = { it.number },
+            )
+
         val OneClickPause =
             AppSwitchPreference<AppPreferences>(
                 title = R.string.one_click_pause,
@@ -909,6 +922,7 @@ val advancedPreferences =
                         // Temporarily disabled, see https://github.com/damontecres/Wholphin/pull/127#issuecomment-3478058418
 //                    AppPreference.NavDrawerSwitchOnFocus,
                         AppPreference.ControllerTimeout,
+                        AppPreference.BackdropStylePref,
                     ),
             ),
         )

app/src/main/java/com/github/damontecres/wholphin/preferences/AppPreferencesSerializer.kt

@@ -91,6 +91,7 @@ class AppPreferencesSerializer
                                 navDrawerSwitchOnFocus =
                                     AppPreference.NavDrawerSwitchOnFocus.defaultValue
                                 showClock = AppPreference.ShowClock.defaultValue
+                                backdropStyle = AppPreference.BackdropStylePref.defaultValue
 
                                 subtitlesPreferences =
                                     SubtitlePreferences