feat: Integrate TaskWarrior with config reading and optimized data

loading

- Read data.location from ~/.config/task/taskrc (supports
  TASKDATA/TASKRC env vars)
- Add get_overview() method to fetch tasks, projects, tags in one call
  (3→1 requests)
- Replace mock data with real TaskWarrior data
- Add logging with env_logger
- Improve tag logging output

src/main.rs

@@ -8,5 +8,10 @@ mod theme;
 mod view;
 
 fn main() {
+    env_logger::Builder::from_default_env()
+        .filter_level(log::LevelFilter::Debug)
+        .init();
+
+    log::info!("Starting Task Warrior GPUI");
     App::run();
 }