Add audio duration and processing factor per minute to dashboard statistics

src/services/stats_service.py

@@ -76,6 +76,26 @@ async def get_usage_stats(db: Session, days: int = 30):
         UsageLog.status == "success"
     ).scalar() or 0
     
+    # Average audio duration
+    avg_duration = db.query(func.avg(UsageLog.duration_seconds)).filter(
+        UsageLog.created_at >= since,
+        UsageLog.status == "success",
+        UsageLog.duration_seconds.isnot(None)
+    ).scalar() or 0
+    
+    # Processing factor (seconds processing time per minute of audio)
+    # Formula: (processing_time_ms / 1000) / duration_seconds * 60
+    processing_factor = db.query(
+        func.avg(
+            (UsageLog.processing_time_ms / 1000.0) / UsageLog.duration_seconds * 60
+        )
+    ).filter(
+        UsageLog.created_at >= since,
+        UsageLog.status == "success",
+        UsageLog.duration_seconds.isnot(None),
+        UsageLog.duration_seconds > 0
+    ).scalar() or 0
+    
     # Daily stats for chart
     daily_stats = db.query(
         func.date(UsageLog.created_at).label("date"),
@@ -96,6 +116,8 @@ async def get_usage_stats(db: Session, days: int = 30):
         "total_requests": total_requests,
         "success_rate": round(success_rate, 2),
         "avg_processing_time_ms": round(avg_time, 2),
+        "avg_duration_seconds": round(avg_duration, 2),
+        "processing_factor": round(processing_factor, 2),
         "daily_stats": [
             {"date": str(stat.date), "count": stat.count, "avg_time": round(stat.avg_time or 0, 2)}
             for stat in daily_stats