Search page improvements (#709)

## Description

Improves how search results are displayed:

- Reorders search categories to Movies → TV Shows → Episodes →
Collections, surfacing the most commonly searched content types at the
top.
- Adds a new "Combined search results" preference in Advanced settings →
Search. When enabled, shows all results in a single list instead of
separate categories.
- When Seerr is active, adds Library/Discover tabs to switch between
local library results and Seerr discovery results.
- Hides empty result categories instead of showing "No results"
placeholders.

### Screenshots

<img width="1935" height="1100" alt="Screenshot_20260116_113656"
src="https://github.com/user-attachments/assets/1e29aa3a-3ba2-4f86-ab61-fed683490474"
/>

<img width="1934" height="1095" alt="image"
src="https://github.com/user-attachments/assets/8b93fa38-d4c9-4e72-a997-caa82b4949f0"
/>

<img width="1921" height="1094" alt="image"
src="https://github.com/user-attachments/assets/82aed1a5-810c-413f-a266-6d78490a1534"
/>

### AI/LLM usage
Code auditing and PR description drafting with Claude Code. Also used
Claude Code for the regex.

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

@@ -66,7 +66,8 @@ class AppPreferencesSerializer
                                             directPlayPgs = AppPreference.DirectPlayPgs.defaultValue
                                             mediaExtensionsEnabled =
                                                 AppPreference.FfmpegPreference.defaultValue
-                                            assPlaybackMode = AppPreference.AssSubtitleMode.defaultValue
+                                            assPlaybackMode =
+                                                AppPreference.AssSubtitleMode.defaultValue
                                         }.build()
 
                                 mpvOptions =
@@ -99,6 +100,13 @@ class AppPreferencesSerializer
                                 backdropStyle = AppPreference.BackdropStylePref.defaultValue
                                 showLogos = AppPreference.ShowLogos.defaultValue
 
+                                searchPreferences =
+                                    SearchPreferences
+                                        .newBuilder()
+                                        .apply {
+                                            combinedSearchResults = false
+                                        }.build()
+
                                 subtitlesPreferences =
                                     SubtitlePreferences
                                         .newBuilder()
@@ -207,6 +215,11 @@ inline fun AppPreferences.updateInterfacePreferences(block: InterfacePreferences
         interfacePreferences = interfacePreferences.toBuilder().apply(block).build()
     }
 
+inline fun AppPreferences.updateSearchPreferences(block: SearchPreferences.Builder.() -> Unit): AppPreferences =
+    updateInterfacePreferences {
+        searchPreferences = searchPreferences.toBuilder().apply(block).build()
+    }
+
 inline fun AppPreferences.updateSubtitlePreferences(block: SubtitlePreferences.Builder.() -> Unit): AppPreferences =
     updateInterfacePreferences {
         subtitlesPreferences = subtitlesPreferences.toBuilder().apply(block).build()