Add task count to task list panel header

Show 'X todo / Y done' in the Tasks panel title bar.

Also includes prior uncommitted work:
- Pagination in fetch_tasks (maxResults=100 + pageToken loop)
- fetch_tasks_since for incremental pull sync
- SyncStats struct with version/last_sync/last_pull/changed counts
- Periodic push (30s) and pull (5min) sync engine
- event::poll(100ms) for non-blocking UI refresh
- Ctrl+R full sync (push + pull)
- refresh_if_needed() to reload data after background sync
- Retry mechanism (MAX_SYNC_RETRIES=3) for sync queue items
- HTTP status code checks in fetch_lists/fetch_tasks/fetch_tasks_since
- Fix move_task URL to use reqwest query()
- Remove CASCADE via replace_all_lists (use insert_list instead)
- has_pending_sync() to prevent pull during pending push

src/infrastructure/db.rs

@@ -37,9 +37,14 @@ impl Db {
                 task_id TEXT NOT NULL,
                 list_id TEXT NOT NULL,
                 payload TEXT NOT NULL,
-                created_at TEXT NOT NULL
+                created_at TEXT NOT NULL,
+                retries INTEGER NOT NULL DEFAULT 0
             );",
         )?;
+        conn.execute_batch(
+            "ALTER TABLE sync_queue ADD COLUMN retries INTEGER NOT NULL DEFAULT 0;",
+        )
+        .ok();
         Ok(Self { conn: Mutex::new(conn) })
     }
 
@@ -201,16 +206,6 @@ impl Db {
         Ok(())
     }
 
-    pub fn replace_all_lists(&self, lists: &[TaskList]) -> SqlResult<()> {
-        let conn = self.conn.lock().unwrap();
-        conn.execute("DELETE FROM task_lists", [])?;
-        drop(conn);
-        for list in lists {
-            self.insert_list(list)?;
-        }
-        Ok(())
-    }
-
     pub fn replace_all_tasks(&self, list_id: &str, tasks: &[Task]) -> SqlResult<()> {
         let conn = self.conn.lock().unwrap();
         conn.execute("DELETE FROM tasks WHERE list_id = ?1", params![list_id])?;
@@ -226,7 +221,27 @@ impl Db {
         Ok(())
     }
 
-    pub fn push_sync(&self, action: SyncAction, task_id: &str, list_id: &str, payload: &str) -> SqlResult<()> {
+    pub fn push_sync(
+        &self,
+        action: SyncAction,
+        task_id: &str,
+        list_id: &str,
+        payload: &str,
+    ) -> SqlResult<()> {
+        self.push_sync_with_retry(action, task_id, list_id, payload, 0)
+    }
+
+    pub fn push_sync_with_retry(
+        &self,
+        action: SyncAction,
+        task_id: &str,
+        list_id: &str,
+        payload: &str,
+        retries: i32,
+    ) -> SqlResult<()> {
+        if retries > MAX_SYNC_RETRIES {
+            return Ok(());
+        }
         let action_str = match action {
             SyncAction::Create => "Create",
             SyncAction::Update => "Update",
@@ -235,24 +250,33 @@ impl Db {
         };
         let conn = self.conn.lock().unwrap();
         conn.execute(
-            "INSERT INTO sync_queue (action, task_id, list_id, payload, created_at)
-             VALUES (?1, ?2, ?3, ?4, ?5)",
+            "INSERT INTO sync_queue (action, task_id, list_id, payload, created_at, retries)
+             VALUES (?1, ?2, ?3, ?4, ?5, ?6)",
             params![
                 action_str,
                 task_id,
                 list_id,
                 payload,
                 chrono::Utc::now().format("%Y-%m-%d %H:%M:%S").to_string(),
+                retries,
             ],
         )?;
         Ok(())
     }
 
+    pub fn has_pending_sync(&self) -> bool {
+        let conn = self.conn.lock().unwrap();
+        let count: i64 = conn
+            .query_row("SELECT COUNT(*) FROM sync_queue", [], |row| row.get(0))
+            .unwrap_or(0);
+        count > 0
+    }
+
     pub fn drain_sync(&self) -> Vec<SyncQueueItem> {
         let conn = self.conn.lock().unwrap();
         let items: Vec<SyncQueueItem> = {
             let mut stmt = conn
-                .prepare("SELECT id, action, task_id, list_id, payload, created_at FROM sync_queue ORDER BY id")
+                .prepare("SELECT id, action, task_id, list_id, payload, created_at, retries FROM sync_queue ORDER BY id")
                 .unwrap();
             stmt.query_map([], |row| {
                 let action_str: String = row.get(1)?;
@@ -270,6 +294,7 @@ impl Db {
                     list_id: row.get(3)?,
                     payload: row.get(4)?,
                     created_at: row.get(5)?,
+                    retries: row.get(6)?,
                 })
             })
             .unwrap()