Add user service discovery to systemd collector

- Use systemctl --user commands to discover user-level services
- Include both user unit files and loaded user units
- Gracefully handle cases where user commands fail (no user session)
- Treat user services same as system services in filtering
- Enables monitoring of user-level Docker, development servers, etc.

agent/src/collectors/systemd.rs

@@ -128,12 +128,45 @@ impl SystemdCollector {
             .arg("--plain")
             .output()?;
 
+        // Also get user unit files (user-level services)
+        let user_unit_files_output = Command::new("systemctl")
+            .arg("--user")
+            .arg("list-unit-files")
+            .arg("--type=service")
+            .arg("--no-pager")
+            .arg("--plain")
+            .output()?;
+
+        // And user loaded units
+        let user_units_output = Command::new("systemctl")
+            .arg("--user")
+            .arg("list-units")
+            .arg("--type=service")
+            .arg("--all")
+            .arg("--no-pager")
+            .arg("--plain")
+            .output()?;
+
         if !unit_files_output.status.success() || !units_output.status.success() {
-            return Err(anyhow::anyhow!("systemctl command failed"));
+            return Err(anyhow::anyhow!("systemctl system command failed"));
         }
 
+        // User commands might fail if no user session, so check individually
+        let user_unit_files_success = user_unit_files_output.status.success();
+        let user_units_success = user_units_output.status.success();
+
         let unit_files_str = String::from_utf8(unit_files_output.stdout)?;
         let units_str = String::from_utf8(units_output.stdout)?;
+        let user_unit_files_str = if user_unit_files_success {
+            String::from_utf8(user_unit_files_output.stdout).ok()
+        } else {
+            None
+        };
+        let user_units_str = if user_units_success {
+            String::from_utf8(user_units_output.stdout).ok()
+        } else {
+            None
+        };
         let mut services = Vec::new();
 
         // Skip setup/certificate services that don't need monitoring (from legacy)
@@ -220,6 +253,28 @@ impl SystemdCollector {
             }
         }
 
+        // Parse user unit files if available
+        if let Some(user_unit_files_str) = &user_unit_files_str {
+            for line in user_unit_files_str.lines() {
+                let fields: Vec<&str> = line.split_whitespace().collect();
+                if fields.len() >= 2 && fields[0].ends_with(".service") {
+                    let service_name = fields[0].trim_end_matches(".service");
+                    all_service_names.insert(service_name.to_string());
+                }
+            }
+        }
+
+        // Parse user loaded units if available
+        if let Some(user_units_str) = &user_units_str {
+            for line in user_units_str.lines() {
+                let fields: Vec<&str> = line.split_whitespace().collect();
+                if fields.len() >= 4 && fields[0].ends_with(".service") {
+                    let service_name = fields[0].trim_end_matches(".service");
+                    all_service_names.insert(service_name.to_string());
+                }
+            }
+        }
+
         // Now process all discovered services
         for service_name in &all_service_names {
                 debug!("Processing service: '{}'", service_name);