feat(storage): add S3 backend support and advanced upload limits

- Introduce S3-compatible storage backend support using minio-go.
- Add configuration options for local storage limits, box limits, and rate limiting.
- Implement storage backend selection (local vs S3) for anonymous and registered users.
- Add an `/admin/storage` management interface.
- Update documentation and environment examples with the new configuration variables.

backend/libs/handlers/security.go

@@ -0,0 +1,78 @@
+package handlers
+
+import (
+	"crypto/rand"
+	"encoding/base64"
+	"net/http"
+	"sync"
+	"time"
+)
+
+const csrfCookieName = "warpbox_csrf"
+
+type rateLimiter struct {
+	mu      sync.Mutex
+	records map[string]rateRecord
+}
+
+type rateRecord struct {
+	StartedAt time.Time
+	Count     int
+}
+
+func newRateLimiter() *rateLimiter {
+	return &rateLimiter{records: make(map[string]rateRecord)}
+}
+
+func (l *rateLimiter) Allow(key string, limit int, window time.Duration, now time.Time) bool {
+	if limit <= 0 || window <= 0 {
+		return true
+	}
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	record := l.records[key]
+	if record.StartedAt.IsZero() || now.Sub(record.StartedAt) >= window {
+		l.records[key] = rateRecord{StartedAt: now, Count: 1}
+		return true
+	}
+	record.Count++
+	l.records[key] = record
+	return record.Count <= limit
+}
+
+func (a *App) csrfToken(w http.ResponseWriter, r *http.Request) string {
+	if cookie, err := r.Cookie(csrfCookieName); err == nil && cookie.Value != "" {
+		return cookie.Value
+	}
+	token := randomToken(32)
+	http.SetCookie(w, &http.Cookie{
+		Name:     csrfCookieName,
+		Value:    token,
+		Path:     "/",
+		HttpOnly: true,
+		SameSite: http.SameSiteLaxMode,
+		Secure:   r.TLS != nil,
+		Expires:  time.Now().Add(12 * time.Hour),
+	})
+	return token
+}
+
+func (a *App) validateCSRF(w http.ResponseWriter, r *http.Request) bool {
+	if r.Method == http.MethodGet || r.Method == http.MethodHead || r.Method == http.MethodOptions {
+		return true
+	}
+	cookie, err := r.Cookie(csrfCookieName)
+	if err != nil || cookie.Value == "" || r.FormValue("csrf_token") != cookie.Value {
+		http.Error(w, "invalid form token", http.StatusForbidden)
+		return false
+	}
+	return true
+}
+
+func randomToken(byteCount int) string {
+	data := make([]byte, byteCount)
+	if _, err := rand.Read(data); err != nil {
+		return base64.RawURLEncoding.EncodeToString([]byte(time.Now().String()))
+	}
+	return base64.RawURLEncoding.EncodeToString(data)
+}