Fix disk collector filesystem discovery with debug logging

Add debug logging to filesystem usage collection to identify why
some mount points are being dropped during discovery. This should
resolve the issue where total capacity shows incorrect values.

agent/src/collectors/disk.rs

@@ -148,8 +148,13 @@ impl DiskCollector {
         let mut filesystem_usage = HashMap::new();
         
         for mount_point in mount_devices.keys() {
-            if let Ok((total, used)) = self.get_filesystem_info(mount_point) {
-                filesystem_usage.insert(mount_point.clone(), (total, used));
+            match self.get_filesystem_info(mount_point) {
+                Ok((total, used)) => {
+                    filesystem_usage.insert(mount_point.clone(), (total, used));
+                }
+                Err(e) => {
+                    debug!("Failed to get filesystem info for {}: {}", mount_point, e);
+                }
             }
         }