Implement comprehensive dashboard improvements and maintenance mode

- Storage widget: Restructure with Name/Temp/Wear/Usage columns, SMART details as descriptions
- Host navigation: Only cycle through connected hosts, no disconnected hosts
- Auto-discovery: Skip config files, use predefined CMTEC host list
- Maintenance mode: Suppress notifications during backup via /tmp/cm-maintenance file
- CPU thresholds: Update to warning ≥9.0, critical ≥10.0 for production use
- Agent-dashboard separation: Agent provides descriptions, dashboard displays only

dashboard/src/app.rs

@@ -469,16 +469,46 @@ impl App {
         usize::try_from(samples.max(1)).unwrap_or(DEFAULT_CAPACITY)
     }
 
+    fn connected_hosts(&self) -> Vec<&HostTarget> {
+        self.hosts
+            .iter()
+            .filter(|host| {
+                self.host_states
+                    .get(&host.name)
+                    .map(|state| state.last_success.is_some())
+                    .unwrap_or(false)
+            })
+            .collect()
+    }
+
     fn select_previous_host(&mut self) {
-        if self.hosts.is_empty() {
+        let connected = self.connected_hosts();
+        if connected.is_empty() {
             return;
         }
 
-        self.active_host_index = if self.active_host_index == 0 {
-            self.hosts.len().saturating_sub(1)
-        } else {
-            self.active_host_index - 1
-        };
+        // Find current host in connected list
+        let current_host = self.hosts.get(self.active_host_index);
+        if let Some(current) = current_host {
+            if let Some(current_pos) = connected.iter().position(|h| h.name == current.name) {
+                let new_pos = if current_pos == 0 {
+                    connected.len().saturating_sub(1)
+                } else {
+                    current_pos - 1
+                };
+                let new_host = connected[new_pos];
+                // Find this host's index in the full hosts list
+                if let Some(new_index) = self.hosts.iter().position(|h| h.name == new_host.name) {
+                    self.active_host_index = new_index;
+                }
+            } else {
+                // Current host not connected, switch to first connected host
+                if let Some(new_index) = self.hosts.iter().position(|h| h.name == connected[0].name) {
+                    self.active_host_index = new_index;
+                }
+            }
+        }
+        
         self.status = format!(
             "Active host switched to {} ({}/{})",
             self.hosts[self.active_host_index].name,
@@ -488,11 +518,29 @@ impl App {
     }
 
     fn select_next_host(&mut self) {
-        if self.hosts.is_empty() {
+        let connected = self.connected_hosts();
+        if connected.is_empty() {
             return;
         }
 
-        self.active_host_index = (self.active_host_index + 1) % self.hosts.len();
+        // Find current host in connected list
+        let current_host = self.hosts.get(self.active_host_index);
+        if let Some(current) = current_host {
+            if let Some(current_pos) = connected.iter().position(|h| h.name == current.name) {
+                let new_pos = (current_pos + 1) % connected.len();
+                let new_host = connected[new_pos];
+                // Find this host's index in the full hosts list
+                if let Some(new_index) = self.hosts.iter().position(|h| h.name == new_host.name) {
+                    self.active_host_index = new_index;
+                }
+            } else {
+                // Current host not connected, switch to first connected host
+                if let Some(new_index) = self.hosts.iter().position(|h| h.name == connected[0].name) {
+                    self.active_host_index = new_index;
+                }
+            }
+        }
+        
         self.status = format!(
             "Active host switched to {} ({}/{})",
             self.hosts[self.active_host_index].name,