feat(security): add trusted proxies and abuse event cleanup

- Add `WARPBOX_TRUSTED_PROXIES` configuration to restrict accepted forwarded client IP headers to specific proxy IPs/CIDRs, securing client IP resolution.
- Integrate `BanService` into the background cleanup job to automatically purge expired abuse and ban evidence events.
- Update documentation with reverse proxy security guidelines and a production systemd deployment guide.

backend/libs/services/proxy.go

@@ -0,0 +1,75 @@
+package services
+
+import (
+	"context"
+	"net"
+	"net/http"
+	"strings"
+)
+
+type clientIPContextKey struct{}
+
+func WithClientIP(r *http.Request, ip string) *http.Request {
+	return r.WithContext(context.WithValue(r.Context(), clientIPContextKey{}, ip))
+}
+
+func ClientIPFromContext(r *http.Request) (string, bool) {
+	ip, ok := r.Context().Value(clientIPContextKey{}).(string)
+	return ip, ok && ip != ""
+}
+
+// ClientIP resolves the effective client IP. When trustedProxies is empty,
+// forwarded headers are trusted for easy reverse-proxy/container defaults.
+func ClientIP(remoteAddr, forwardedFor, realIP string, trustedProxies []string) string {
+	remoteIP := remoteIPOnly(remoteAddr)
+	if len(trustedProxies) == 0 || remoteTrusted(remoteIP, trustedProxies) {
+		if ip := firstForwardedIP(forwardedFor); ip != "" {
+			return ip
+		}
+		if ip := strings.TrimSpace(realIP); ip != "" {
+			return ip
+		}
+	}
+	return remoteIP
+}
+
+func remoteIPOnly(remoteAddr string) string {
+	host := strings.TrimSpace(remoteAddr)
+	if splitHost, _, err := net.SplitHostPort(remoteAddr); err == nil {
+		host = splitHost
+	}
+	return strings.Trim(host, "[]")
+}
+
+func firstForwardedIP(forwardedFor string) string {
+	for _, part := range strings.Split(forwardedFor, ",") {
+		ip := strings.TrimSpace(part)
+		if ip != "" {
+			return strings.Trim(ip, "[]")
+		}
+	}
+	return ""
+}
+
+func remoteTrusted(remoteIP string, trustedProxies []string) bool {
+	parsed := net.ParseIP(remoteIP)
+	if parsed == nil {
+		return false
+	}
+	for _, trusted := range trustedProxies {
+		trusted = strings.TrimSpace(trusted)
+		if trusted == "" {
+			continue
+		}
+		if strings.Contains(trusted, "/") {
+			if _, network, err := net.ParseCIDR(trusted); err == nil && network.Contains(parsed) {
+				return true
+			}
+			continue
+		}
+		if ip := net.ParseIP(trusted); ip != nil && ip.Equal(parsed) {
+			return true
+		}
+	}
+	return false
+}