Add in-app & Android TV screensaver (#946)

## Description
Adds both an optional in-app and Android TV OS (DreamService)
screensaver

Has settings for:
- Starting delay, options from 30s to 1 hour
- Duration to show each image, 30s to 2 minutes
- Show clock (separate from app-wide clock)
- Toggle animated zooming
- Set a max age rating to limit what content is shown
- Included media types: movies, tv shows, and/or photos

By default only Movies & TV Shows are included. But if you have like
family albums on your server, you could enable Photos too.

There's also an button to start the screensaver so you can see what it
looks like.

### Related issues
Closes #230

### Testing
Emulator, Onn 4k pro, nvidia shield using both in-app and OS
screensavers

## Screenshots
![screensaver_settings
Large](https://github.com/user-attachments/assets/9b3240dd-81cb-4c20-bc4e-b2bf38698b2f)

## AI or LLM usage
None

## Acknowledgements

Some of the skeleton code for setting up the `DreamService` with the
right lifecycle was copied and modified from the [official app's
implementation](https://github.com/jellyfin/jellyfin-androidtv/blob/master/app/src/main/java/org/jellyfin/androidtv/integration/dream/DreamServiceCompat.kt).

app/src/main/proto/WholphinDataStore.proto

@@ -144,6 +144,16 @@ enum BackdropStyle{
   BACKDROP_NONE = 2;
 }
 
+message ScreensaverPreferences{
+  int64 start_delay = 1;
+  int64 duration = 2;
+  bool animate = 3;
+  int32 max_age_filter = 4;
+  bool enabled = 5;
+  repeated string item_types = 6;
+  bool show_clock = 7;
+}
+
 message InterfacePreferences {
   ThemeSongVolume play_theme_songs = 1;
   bool remember_selected_tab = 2;
@@ -155,6 +165,7 @@ message InterfacePreferences {
   LiveTvPreferences live_tv_preferences = 8;
   BackdropStyle backdrop_style = 9;
   SubtitlePreferences hdr_subtitles_preferences = 10;
+  ScreensaverPreferences screensaver_preference = 11;
 }
 
 message AdvancedPreferences {