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/task/model.rs

@@ -214,3 +214,13 @@ pub struct TaskUpdate {
     pub annotations: Option<Vec<String>>,
     pub dependencies: Option<Vec<String>>,
 }
+
+#[derive(Debug, Clone)]
+pub struct TaskOverview {
+    pub tasks: Vec<Task>,
+    pub projects: Vec<(String, usize)>,
+    pub tags: Vec<(String, usize)>,
+    pub total_tasks: usize,
+    pub pending_tasks: usize,
+    pub completed_tasks: usize,
+}