feat: add host restart detection and fix agent version display

Potential fixes for issues #4 and #6.

Agent version display:
- Set CurrentVersion during registration instead of waiting for first check-in
- Update UI to show "Initial Registration" instead of "Unknown"

Host restart detection:
- Added reboot_required, last_reboot_at, reboot_reason fields to agents table
- Agent now detects pending reboots (Debian/Ubuntu via /var/run/reboot-required, RHEL/Fedora via needs-restarting)
- New reboot command type with 1-minute grace period
- UI shows restart alerts and adds restart button in quick actions
- Restart indicator badge in agent list

The reboot detection runs during system info collection and gets reported back to the server automatically.

Using shutdown command for now until we make the restart mechanism user-adjustable later - need to think on that.
Also need to come up with a Windows derivative outside of reading event log for detecting reboots.

aggregator-agent/internal/system/info.go

@@ -21,6 +21,8 @@ type SystemInfo struct {
 	DiskInfo       []DiskInfo        `json:"disk_info"`
 	RunningProcesses int             `json:"running_processes"`
 	Uptime         string            `json:"uptime"`
+	RebootRequired bool              `json:"reboot_required"`
+	RebootReason   string            `json:"reboot_reason"`
 	Metadata       map[string]string `json:"metadata"`
 }
 
@@ -113,6 +115,11 @@ func GetSystemInfo(agentVersion string) (*SystemInfo, error) {
 		}
 	}
 
+	// Check if system requires reboot
+	rebootRequired, rebootReason := checkRebootRequired()
+	info.RebootRequired = rebootRequired
+	info.RebootReason = rebootReason
+
 	// Add collection timestamp
 	info.Metadata["collected_at"] = time.Now().Format(time.RFC3339)
 
@@ -467,4 +474,64 @@ func GetLightweightMetrics() (*LightweightMetrics, error) {
 	// In the future, we could add a background goroutine to track CPU usage
 
 	return metrics, nil
-}
+}
+// checkRebootRequired checks if the system requires a reboot
+func checkRebootRequired() (bool, string) {
+	if runtime.GOOS == "linux" {
+		return checkLinuxRebootRequired()
+	} else if runtime.GOOS == "windows" {
+		return checkWindowsRebootRequired()
+	}
+	return false, ""
+}
+
+// checkLinuxRebootRequired checks if a Linux system requires a reboot
+func checkLinuxRebootRequired() (bool, string) {
+	// Method 1: Check Debian/Ubuntu reboot-required file
+	if err := exec.Command("test", "-f", "/var/run/reboot-required").Run(); err == nil {
+		// File exists, reboot is required
+		// Try to read the packages that require reboot
+		if output, err := exec.Command("cat", "/var/run/reboot-required.pkgs").Output(); err == nil {
+			packages := strings.TrimSpace(string(output))
+			if packages != "" {
+				// Truncate if too long
+				if len(packages) > 200 {
+					packages = packages[:200] + "..."
+				}
+				return true, "Packages: " + packages
+			}
+		}
+		return true, "System updates require reboot"
+	}
+
+	// Method 2: Check RHEL/Fedora/Rocky using needs-restarting
+	cmd := exec.Command("needs-restarting", "-r")
+	if err := cmd.Run(); err != nil {
+		if exitErr, ok := err.(*exec.ExitError); ok {
+			// Exit code 1 means reboot is needed
+			if exitErr.ExitCode() == 1 {
+				return true, "Kernel or system libraries updated"
+			}
+		}
+	}
+
+	return false, ""
+}
+
+// checkWindowsRebootRequired checks if a Windows system requires a reboot
+func checkWindowsRebootRequired() (bool, string) {
+	// Check Windows Update pending reboot registry keys
+	// HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate\Auto Update\RebootRequired
+	cmd := exec.Command("reg", "query", "HKLM\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\WindowsUpdate\\Auto Update\\RebootRequired")
+	if err := cmd.Run(); err == nil {
+		return true, "Windows updates require reboot"
+	}
+
+	// Check Component Based Servicing pending reboot
+	cmd = exec.Command("reg", "query", "HKLM\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Component Based Servicing\\RebootPending")
+	if err := cmd.Run(); err == nil {
+		return true, "Component updates require reboot"
+	}
+
+	return false, ""
+}