feat(balancer): add balancer-to-balancer fallback support (#5586)

* feat(balancer): add balancer-to-balancer fallback support

Xray does not natively support using a balancer as fallbackTag for
another balancer. This feature automates the loopback workaround:
when a user selects a balancer as fallback, the panel generates a
loopback outbound + routing rule in the template.

How it works:
- User picks fallback balancer from dropdown
- Panel creates loopback outbound _bl_{target} + routing rule
- Balancer fallbackTag set to _bl_{target}
- Traffic: Balancer A → loopback _bl_B → routing rule → Balancer B

Key features:
- Dedup: multiple balancers sharing same fallback reuse one loopback
- DFS cycle detection at edit time and on save
- Self-reference guard (cannot select own balancer)
- Delete protection (blocks if used as fallback by others)
- Cleans up routing rules referencing deleted balancers
- Override resolves balancer tags through loopback mechanism
- All live status tags resolved for display
- Internal _bl_ objects filtered from Outbounds/Routing UI
- Backward-compatible with old _bl_ naming format
- Translations for all 13 locales

* fix(review): override regression, save payload sync, i18n completeness

- OverrideBalancer: only resolve to loopback when resolution succeeds,
  pass original target through for plain outbound tags
- onSaveAll: serialize cleaned template before save to ensure the
  healed/cleaned config is what gets persisted
- Add reservedPrefix translation key to all 12 non-English locales
- Restore trailing newlines in all 13 translation JSON files

* fix(test): update balancer form modal tests after cycle-detection guard

The okButtonProps disabled guard (added in 56d5825c) prevents the modal
from firing onOk when the form is invalid. The old tests clicked the
button expecting validation errors to appear, but antd Modal never calls
onOk on a disabled button — causing false failures.

Rewrite to test the actual guard behavior:
- Button starts disabled (empty form)
- Stays disabled with tag only (selector still empty)
- Stays disabled for duplicate tag
- Disabled button does not trigger onConfirm

---------

Co-authored-by: MHSanaei <ho3ein.sanaei@gmail.com>

internal/web/translation/fa-IR.json

@@ -1755,6 +1755,7 @@
         "tagPlaceholder": "تگ منحصربه‌فرد بالانسر",
         "selector": "انتخابگر",
         "fallback": "Fallback",
+        "cycleTooltip": "حلقه: {path} → (بازگشت به {start})",
         "expected": "مورد انتظار",
         "expectedPlaceholder": "تعداد نود بهینه",
         "maxRtt": "حداکثر RTT",
@@ -1764,7 +1765,12 @@
         "balancerDesc": "امکان استفاده همزمان balancerTag و outboundTag باهم وجود ندارد. درصورت استفاده همزمان فقط outboundTag عمل خواهد کرد.",
         "costMatch": "الگوی برچسب",
         "costValue": "وزن",
-        "costRegexp": "تطبیق با عبارت باقاعده"
+        "costRegexp": "تطبیق با عبارت باقاعده",
+        "balancerDeleteInUse": "امکان حذف این بالانسر وجود ندارد — به عنوان پشتیبان برای موارد زیر استفاده می‌شود: {names}",
+        "balancerFallbackCycle": "امکان تنظیم این بالانسر به عنوان پشتیبان وجود ندارد — وابستگی دایره‌ای ایجاد می‌کند.",
+        "balancerFallbackInfo": "ترافیک از مسیر زیر مسیریابی می‌شود: بالانسر → Loopback → سرور → بالانسر مقصد → اتصال خروجی. این یک پرش اضافی از طریق سرور اضافه می‌کند که ممکن است تأخیرهای جزئی ایجاد کند.",
+        "fallbackBalancerHint": "یک بالانسر دیگر به عنوان پشتیبان انتخاب کنید",
+        "reservedPrefix": "پیشوند _bl_ برای اشیاء loopback داخلی بالانسر رزرو شده است"
       },
       "wireguard": {
         "secretKey": "کلید شخصی",