Add getUsageStats operation + hook

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/operations/usage_stats.gql

@@ -0,0 +1,26 @@
+query getUsageStats($days: Int! = 30) {
+  getUsageStats(days: $days) {
+    totalUsers
+    totalVideos
+    totalShots
+    totalRuns
+    windows {
+      label
+      newUsers
+      activeUsers
+      sessions
+      shots
+    }
+    daily {
+      day
+      newUsers
+      activeUsers
+      sessions
+      shots
+    }
+    processingLast24h {
+      status
+      count
+    }
+  }
+}