v0.1.17: security hardening — 18/20 vulnerabilities fixed

Phase 1 (Critical):
- #1 JWT auth (done in v0.1.16)
- #2 Batch message size validation in send_message_batch.go
- #10 RLock in GetQueueUrlV1 (data race fix)

Phase 2 (AWS-compatible limits):
- #3 QueueName validation: max 80 chars, [a-zA-Z0-9_-](.fifo)?
- #4 WaitTimeSeconds clamped to 0-20
- #5 ReceiveMessageWaitTimeSeconds clamped to 0-20
- #6 DelaySeconds clamped to 0-900
- #7 VisibilityTimeout clamped to 0-43200
- #8 MaxNumberOfMessages clamped to 1-10
- #9 Message attributes limited to 10 per message
- #15 BatchEntryId length validated (max 80)
- #16 DeduplicationID length validated (max 128)
- #17 GroupID length validated (max 128)

Phase 3 (Per-tenant resource limits):
- #11 Max messages per queue (120K standard, 20K FIFO)
- #12 Global tenant limit (1000)
- #3.5 HTTP request body size limit (1MB via MaxBytesReader)

Phase 4 (Stability):
- #14 Duplicates map cleanup (already in PeriodicTasks)
- #13 FIFO group lock timeout (already in visibility timeout reset)
- #18 Redis size guard: skip save if >50MB

Skipped (Low, no real risk):
- #19 {account} URL param (informational only, not used for access)
- #20 ReceiptHandle format (self-validating UUID#UUID)

New file: app/gosqs/validation.go — centralized AWS SQS limits and validators

app/persistence/redis.go

@@ -80,6 +80,11 @@ func SaveQueue(key string, queue *models.Queue) {
 		log.Errorf("persistence: marshal queue %q: %v", key, err)
 		return
 	}
+	// Fix #4.3: Redis size guard — не сохранять если > 50MB (OOM protection)
+	if len(data) > 50*1024*1024 {
+		log.Warnf("persistence: queue %q too large for Redis (%d bytes), skipping", key, len(data))
+		return
+	}
 	asyncWrite(func() {
 		ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
 		defer cancel()