Fix N+1 query performance issue in schedule list endpoint

Replace inefficient loop with N database queries (1 + N schedules) with
optimized single query approach. Reduces database load and improves
response times for /api/schedule endpoint when fetching all schedules.

- Add ScheduleService::list_all_schedule_data_v1() method for single query
- Update handler to use optimized method instead of per-schedule queries
- Maintains identical API response format
- Scales better as schedule data grows

src/handlers/schedule.rs

@@ -20,15 +20,8 @@ pub async fn get_schedule(
             })))
         },
         None => {
-            // Return all schedules when no date specified
-            let schedules = ScheduleService::list_schedules_v1(&state.pool).await?;
-            let mut schedule_data_list = Vec::new();
-            
-            for schedule in schedules {
-                let date_str = schedule.date.format("%Y-%m-%d").to_string();
-                let schedule_data = ScheduleService::get_schedule_data_v1(&state.pool, &date_str).await?;
-                schedule_data_list.push(schedule_data);
-            }
+            // Return all schedules when no date specified - single query optimization
+            let schedule_data_list = ScheduleService::list_all_schedule_data_v1(&state.pool).await?;
             
             Ok(Json(serde_json::json!({
                 "success": true,

src/services/schedule.rs

@@ -119,6 +119,33 @@ impl ScheduleService {
         convert_schedules_to_v1(schedules)
     }
 
+    /// Get all schedule data in ScheduleData format (optimized single query)
+    pub async fn list_all_schedule_data_v1(pool: &PgPool) -> Result<Vec<ScheduleData>> {
+        let schedules = schedule::list_all_schedules(pool).await?;
+        
+        let mut schedule_data_list = Vec::new();
+        for schedule in schedules {
+            let personnel = Personnel {
+                ss_leader: schedule.ss_leader.unwrap_or_default(),
+                ss_teacher: schedule.ss_teacher.unwrap_or_default(),
+                mission_story: schedule.mission_story.unwrap_or_default(),
+                song_leader: schedule.song_leader.unwrap_or_default(),
+                announcements: schedule.scripture.unwrap_or_default(),
+                offering: schedule.offering.unwrap_or_default(),
+                special_music: schedule.special_music.unwrap_or_default(),
+                speaker: schedule.sermon_speaker.unwrap_or_default(),
+                deacons: schedule.deacons.unwrap_or_default(),
+            };
+
+            schedule_data_list.push(ScheduleData {
+                date: schedule.date.format("%Y-%m-%d").to_string(),
+                personnel,
+            });
+        }
+        
+        Ok(schedule_data_list)
+    }
+
     // V2 API methods (UTC timezone as per shared converter)
 
     /// Get schedule by date with V2 format (UTC timestamps)