Improve widget formatting and add logged-in users support

Services widget:
- Fix disk quota formatting with proper rounding instead of truncation
- Remove decimals from RAM quotas and use GB instead of G
- Change quota display to use GB consistently

Backups widget:
- Change GiB to GB for consistency
- Remove spaces between numbers and units
- Update disk usage format to match other widgets: used (totalGB)
- Remove percentage display for cleaner format

System widget:
- Add support for logged-in users in description lines
- Format C-states with "C-State:" prefix on first line, indent subsequent lines
- Add logged_in_users field to SystemSummary data structure

Documentation:
- Add example hash error output to NixOS update instructions

dashboard/src/data/metrics.rs

@@ -58,6 +58,8 @@ pub struct SystemSummary {
     pub cpu_temp_status: Option<String>,
     #[serde(default)]
     pub cpu_cstate: Option<Vec<String>>,
+    #[serde(default)]
+    pub logged_in_users: Option<Vec<String>>,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]

dashboard/src/ui/backup.rs

@@ -59,11 +59,11 @@ fn render_metrics(frame: &mut Frame, _host: &HostDisplayData, metrics: &BackupMe
 
     data.add_row(
         Some(WidgetStatus::new(latest_status)),
-        vec![format!("{} archives, {:.1} GiB total", metrics.backup.snapshot_count, metrics.backup.size_gb)],
+        vec![format!("{} archives, {:.1}GB total", metrics.backup.snapshot_count, metrics.backup.size_gb)],
         vec![
             "Latest".to_string(),
             latest_time,
-            format!("{:.1} GiB", metrics.backup.latest_archive_size_gb.unwrap_or(metrics.backup.size_gb)),
+            format!("{:.1}GB", metrics.backup.latest_archive_size_gb.unwrap_or(metrics.backup.size_gb)),
         ],
     );
 
@@ -81,7 +81,15 @@ fn render_metrics(frame: &mut Frame, _host: &HostDisplayData, metrics: &BackupMe
             vec![
                 "Disk".to_string(),
                 disk.health.clone(),
-                format!("{:.1}/{:.0} GB ({:.0}%)", disk.used_gb, disk.total_gb, disk.usage_percent),
+                {
+                    let used_mb = disk.used_gb * 1000.0;
+                    let used_str = if used_mb < 1000.0 {
+                        format!("{:.0}MB", used_mb)
+                    } else {
+                        format!("{:.1}GB", disk.used_gb)
+                    };
+                    format!("{} ({}GB)", used_str, disk.total_gb.round() as u32)
+                },
             ],
         );
     } else {

dashboard/src/ui/services.rs

@@ -154,13 +154,8 @@ fn format_memory_value(used: f32, quota: f32) -> String {
     
     if quota > 0.05 {
         let quota_gb = quota / 1000.0;
-        // Format quota nicely - show decimals only if needed
-        let quota_str = if quota_gb.fract() == 0.0 {
-            format!("{}G", quota_gb as u32)
-        } else {
-            format!("{:.1}G", quota_gb)
-        };
-        format!("{} ({})", used_value, quota_str)
+        // Format quota without decimals and use GB
+        format!("{} ({}GB)", used_value, quota_gb as u32)
     } else {
         used_value
     }
@@ -178,13 +173,8 @@ fn format_disk_value(used: f32, quota: f32) -> String {
     let used_value = format_bytes(used * 1000.0); // Convert GB to MB for format_bytes
     
     if quota > 0.05 {
-        // Format quota nicely - show decimals only if needed
-        let quota_str = if quota.fract() == 0.0 {
-            format!("{}G", quota as u32)
-        } else {
-            format!("{:.1}G", quota)
-        };
-        format!("{} ({})", used_value, quota_str)
+        // Format quota without decimals and use GB (round to nearest GB)
+        format!("{} ({}GB)", used_value, quota.round() as u32)
     } else {
         used_value
     }

dashboard/src/ui/system.rs

@@ -65,12 +65,35 @@ fn render_metrics(
         overall_status.clone()
     );
 
-    // Use agent-provided C-states as description (agent decides what goes in descriptions)
-    let cstate_description = summary.cpu_cstate.clone().unwrap_or_default();
+    // Use agent-provided C-states and logged-in users as description
+    let mut description_lines = Vec::new();
+    
+    // Add C-states with prefix on first line, indent subsequent lines
+    if let Some(cstates) = &summary.cpu_cstate {
+        for (i, cstate_line) in cstates.iter().enumerate() {
+            if i == 0 {
+                description_lines.push(format!("C-State: {}", cstate_line));
+            } else {
+                description_lines.push(format!("         {}", cstate_line));
+            }
+        }
+    }
+    
+    // Add logged-in users to description
+    if let Some(users) = &summary.logged_in_users {
+        if !users.is_empty() {
+            let user_line = if users.len() == 1 {
+                format!("Logged in: {}", users[0])
+            } else {
+                format!("Logged in: {} users ({})", users.len(), users.join(", "))
+            };
+            description_lines.push(user_line);
+        }
+    }
 
     system_dataset.add_row(
         overall_status.clone(),
-        cstate_description,
+        description_lines,
         vec![
             format!("{:.1} / {:.1} GB", summary.memory_used_mb / 1000.0, summary.memory_total_mb / 1000.0),
             format!("{:.2} • {:.2} • {:.2}", summary.cpu_load_1, summary.cpu_load_5, summary.cpu_load_15),