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/res/values/strings.xml

@@ -445,6 +445,10 @@
     <string name="color_code_programs">Color-code programs</string>
     <string name="subtitle_delay">Subtitle delay</string>
     <string name="backdrop_display">Backdrop style</string>
+    <string name="combined_search_results">Combined search results</string>
+    <string name="combined_search_results_on">Show all results in a single list</string>
+    <string name="combined_search_results_off">Show results by category</string>
+    <string name="results">Results</string>
     <string name="resolution_switching">Resolution switching</string>
     <string name="local">Local</string>
     <string name="play_trailer">Play trailer</string>