Add search input to tracker list

Heya Dustin, been a while, hope all is well in your world! 👋 I'm sometimes frustrated that I can't find my own server in the tracker list, so I took a stab at adding a search input to the tracker listing to match the functionality in the original client: <img width="622" height="489" alt="Screenshot 2025-09-19 at 4 47 00 PM" src="https://github.com/user-attachments/assets/11d731e5-17f3-49f7-bc0d-5c2b546b2622" /> In this PR change, the new input looks like: <img width="1195" height="974" alt="Screenshot 2025-09-19 at 5 22 24 PM" src="https://github.com/user-attachments/assets/6d0cbe56-b8a2-4349-9aac-6181a4deed92" /> <img width="1195" height="974" alt="Screenshot 2025-09-19 at 5 22 28 PM" src="https://github.com/user-attachments/assets/b51d374e-024c-4244-a418-9f033dc4fbc3" /> I also fixed two issues I ran into with the tracker list. 1. The tracker list would collapse when the app loses focus, or when a refresh timer fires. Fixed in https://github.com/mierau/hotline/commit/af6ea9e7c21883337a360c3d61501469e3091353. 2. The tracker list was expanded by default, but empty. Fixed in https://github.com/mierau/hotline/commit/43306c40b51507061cde05acb1eb95db611c50e8