style(gamification): drop em-dash from cascade comment

Matches the project's style preference for full stops over em/en dashes.
No functional change.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/storage/src/database.rs

@@ -452,7 +452,7 @@ pub async fn complete_subtask_and_check_parent(pool: &SqlitePool, subtask_id: &s
 
         if pending == 0 {
             // Phase 8: flag the cascade so the daily-count query can exclude
-            // it. The subtask UPDATE (above) stays at auto_completed = 0 — the
+            // it. The subtask UPDATE (above) stays at auto_completed = 0. The
             // user explicitly ticked it, so it counts.
             sqlx::query(
                 "UPDATE tasks SET done = 1, done_at = datetime('now'), auto_completed = 1 \