feat(nodes): add per-node TLS verification mode for self-signed certs (#4757)

Adds a per-node TLS verification mode to the Add/Edit Node dialog so the panel can reach nodes that serve HTTPS with a self-signed certificate:

- verify (default): normal CA validation.
- skip: InsecureSkipVerify, with a clear UI warning that it drops MITM protection.
- pin: validates the leaf certificate's SHA-256 (base64 or hex) via VerifyConnection while bypassing the default chain/name check — keeps MITM protection for self-signed certs, the secure alternative to skip.

New Node model fields tlsVerifyMode + pinnedCertSha256 (gorm auto-migrated). Probe() selects the HTTP client per node via nodeHTTPClientFor, keeping the SSRF-guarded dialer. A new POST /panel/api/nodes/certFingerprint endpoint (FetchCertFingerprint) lets the UI fetch and pin the node's current certificate in one click. Endpoint documented in api-docs/openapi; i18n added across all locales. Verified end-to-end in Docker (verify rejects, skip bypasses, fetch matches, pin accepts correct / rejects wrong).

web/translation/id-ID.json

@@ -869,7 +869,19 @@
         "updateStarted": "Pembaruan panel dimulai",
         "updateResult": "Pembaruan dipicu pada {ok} node, {failed} gagal",
         "updateNoneEligible": "Pilih minimal satu node online dan aktif"
-      }
+      },
+      "tlsVerifyMode": "Verifikasi TLS",
+      "tlsVerifyModeHint": "Cara panel memvalidasi sertifikat HTTPS node. Pin atau Lewati untuk sertifikat self-signed (hanya node https).",
+      "tlsVerify": "Verifikasi (CA bawaan)",
+      "tlsPin": "Pin sertifikat (SHA-256)",
+      "tlsSkip": "Lewati verifikasi",
+      "tlsSkipWarning": "Melewati verifikasi menghilangkan perlindungan terhadap serangan man-in-the-middle — token API bisa disadap. Lebih baik pin sertifikat.",
+      "pinnedCert": "SHA-256 sertifikat yang dipin",
+      "pinnedCertHint": "SHA-256 sertifikat node dalam base64 atau hex. Gunakan Ambil untuk membacanya dari node sekarang.",
+      "pinnedCertPlaceholder": "SHA-256 base64 atau hex",
+      "fetchPin": "Ambil",
+      "pinFetched": "Berhasil mengambil sertifikat node saat ini",
+      "pinFetchFailed": "Tidak dapat mengambil sertifikat"
     },
     "settings": {
       "title": "Pengaturan Panel",