Enhance disk collector with individual drive health monitoring

- Add StoragePool and DriveInfo structures for grouping drives by mount point
- Implement SMART data collection for individual drives (health, temperature, wear)
- Support for ext4, zfs, xfs, mergerfs, btrfs filesystem types
- Generate individual drive metrics: disk_[pool]_[drive]_health/temperature/wear
- Add storage_type and underlying_devices to filesystem configuration
- Move hardcoded service directory mappings to NixOS configuration
- Move hardcoded host-to-user mapping to NixOS configuration
- Remove all unused code and fix compilation warnings
- Clean implementation with zero warnings and no dead code

Individual drives now show health status per storage pool:
Storage root (ext4): nvme0n1 PASSED 42°C 5% wear
Storage steampool (mergerfs): sda/sdb/sdc with individual health data

agent/src/metrics/mod.rs

@@ -51,7 +51,7 @@ impl MetricCollectionManager {
             }
             Some("systemd") => {
                 // Systemd collector only
-                let systemd_collector = SystemdCollector::new();
+                let systemd_collector = SystemdCollector::new(config.systemd.clone());
                 collectors.push(Box::new(systemd_collector));
                 info!("BENCHMARK: Systemd collector only");
             }
@@ -88,7 +88,7 @@ impl MetricCollectionManager {
                 collectors.push(Box::new(disk_collector));
                 info!("Disk collector initialized");
 
-                let systemd_collector = SystemdCollector::new();
+                let systemd_collector = SystemdCollector::new(config.systemd.clone());
                 collectors.push(Box::new(systemd_collector));
                 info!("Systemd collector initialized");