feat(balancers): tabbed Observatory/Burst Observatory form (#5627)

* feat(balancers): tabbed Observatory/Burst form replacing raw JSON

Replace the raw JSON editor for the Observatory / Burst Observatory sections
with a proper Ant Design form, and split the Balancers page into two sub-tabs:
"Balancer Settings" (the existing table) and "Observatory".

Observers stay fully auto-managed by balancer strategy through the existing
syncObservatories logic: users edit only the tunable probe fields, the
subjectSelector is shown read-only since it is derived from the balancers, and
deleting the last balancer that needs an observer now warns in the confirm
dialog that the observer will be removed too. Overlapping selectors keep an
observer alive while any balancer still references it.

Also add the previously missing pingConfig.httpMethod field (HEAD/GET) and
translations for the new strings across all 13 locales.

* refactor(balancers): tighten httpMethod typing and align connectivity default

Address automated review feedback on the Observatory form:
- Use the ObservatoryHttpMethodSchema enum for pingConfig.httpMethod instead of
  a free-form z.string(), and drive the HTTP method Select from its options.
  Removes the previously dead enum export and the duplicate local list, and
  types the field as 'HEAD' | 'GET'.
- Align the schema's connectivity default with DEFAULT_BURST_OBSERVATORY (the
  hicloud URL) so it matches what burst observers are actually created with.

No behavior change.

internal/web/translation/id-ID.json

@@ -1663,6 +1663,36 @@
         "toastDeleted": "Dihapus",
         "toastDeleteFailed": "Gagal menghapus"
       },
+      "tabBalancerSettings": "Pengaturan Balancer",
+      "tabObservatory": "Observatory",
+      "observatory": {
+        "title": "Observatory",
+        "burstTitle": "Burst Observatory",
+        "autoManaged": "Observer dikelola otomatis dari balancer Anda. Atur cara mereka melakukan probe di bawah; outbound yang dipantau mengikuti selector balancer.",
+        "emptyHint": "Tidak ada observer koneksi yang aktif. Satu akan ditambahkan otomatis saat Anda membuat balancer Least Ping atau Least Load — atau balancer Random / Round-robin dengan fallback — sehingga balancer dapat mengukur outbound Anda dan memilih yang terbaik.",
+        "subjectSelector": "Outbound yang Dipantau",
+        "subjectSelectorDesc": "Tag outbound yang di-probe observer ini. Dikelola otomatis dari balancer Anda.",
+        "probeURL": "URL Probe",
+        "probeURLDesc": "URL yang diminta untuk mengukur setiap outbound. Harus mengembalikan HTTP 204.",
+        "probeInterval": "Interval Probe",
+        "probeIntervalDesc": "Seberapa sering memprobe tiap outbound, mis. 30s, 1m, 2h45m.",
+        "enableConcurrency": "Probe Bersamaan",
+        "enableConcurrencyDesc": "Probe semua outbound yang dipantau sekaligus, bukan satu per satu. Lebih cepat, tetapi lebih terlihat di jaringan.",
+        "destination": "Tujuan Probe",
+        "destinationDesc": "URL yang diminta untuk mengukur setiap outbound. Harus mengembalikan HTTP 204.",
+        "connectivity": "Pemeriksaan Konektivitas",
+        "connectivityDesc": "URL pemeriksaan jaringan lokal opsional, dicoba hanya setelah tujuan gagal. Kosongkan untuk melewati.",
+        "interval": "Interval Probe",
+        "intervalDesc": "Rata-rata waktu antar probe per outbound, mis. 1m. Minimal 10s.",
+        "timeout": "Batas Waktu Probe",
+        "timeoutDesc": "Berapa lama menunggu probe sebelum dianggap gagal, mis. 5s.",
+        "sampling": "Jumlah Sampling",
+        "samplingDesc": "Jumlah hasil probe terbaru yang disimpan untuk menilai tiap outbound.",
+        "httpMethod": "Metode HTTP",
+        "httpMethodDesc": "Metode HTTP yang digunakan untuk probe.",
+        "deleteAlsoObservatory": "Ini balancer terakhir yang memakai Observatory, jadi itu juga akan dihapus.",
+        "deleteAlsoBurst": "Ini balancer terakhir yang memakai Burst Observatory, jadi itu juga akan dihapus."
+      },
       "balancer": {
         "addBalancer": "Tambahkan Penyeimbang",
         "editBalancer": "Sunting Penyeimbang",