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/build.gradle.kts

@@ -223,6 +223,7 @@ dependencies {
     implementation(libs.androidx.hilt.navigation.compose)
     implementation(libs.androidx.preference.ktx)
     implementation(libs.androidx.room.testing)
+    implementation(libs.androidx.palette.ktx)
     ksp(libs.androidx.room.compiler)
     ksp(libs.hilt.android.compiler)