Add certbot status to dashboard services and sidebar nav indicator

- Add certbot to getDaemonStatus: checks binary availability and version
- Dashboard: add Certificates card to services grid
- Sidebar: show green/red status dot for certbot on Certificates nav item

internal/api/v1/handlers.go

@@ -550,6 +550,20 @@ func getDaemonStatus() map[string]map[string]any {
 	}
 	result["nftables"] = nftEntry
 
+	// certbot is a CLI tool, not a daemon — check if installed
+	certbotEntry := map[string]any{"active": false}
+	if _, err := exec.LookPath("certbot"); err == nil {
+		certbotEntry["active"] = true
+		if out, verErr := exec.Command("certbot", "--version").Output(); verErr == nil {
+			// "certbot 2.11.0"
+			s := strings.TrimSpace(string(out))
+			if _, after, found := strings.Cut(s, " "); found {
+				certbotEntry["version"] = after
+			}
+		}
+	}
+	result["certbot"] = certbotEntry
+
 	return result
 }