refactor: convert from Android TV to phone/tablet mode

- Replace Theme.Leanback with Theme.AppCompat.DayNight.NoActionBar
- Remove leanback dependencies (leanback, leanback-preference)
- Remove LEANBACK_LAUNCHER, leanback feature, banner from manifest
- PlayerActivity: replace D-pad with touch controls (click to toggle episodes, close button)
- SearchFragment: adaptive grid (3 cols phone / 5 cols tablet), remove focus-based history toggle
- Fix deprecated adapterPosition -> bindingAdapterPosition

app/build.gradle.kts

@@ -41,10 +41,6 @@ android {
 }
 
 dependencies {
-    // Leanback (TV UI)
-    implementation("androidx.leanback:leanback:1.0.0")
-    implementation("androidx.leanback:leanback-preference:1.0.0")
-
     // AndroidX
     implementation("androidx.core:core-ktx:1.12.0")
     implementation("androidx.appcompat:appcompat:1.6.1")