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/ja-JP.json

@@ -869,7 +869,19 @@
         "updateStarted": "パネルの更新を開始しました",
         "updateResult": "{ok} 個のノードで更新を開始、{failed} 個失敗",
         "updateNoneEligible": "オンラインで有効なノードを少なくとも1つ選択してください"
-      }
+      },
+      "tlsVerifyMode": "TLS 検証",
+      "tlsVerifyModeHint": "パネルがノードの HTTPS 証明書を検証する方法。ピン留めやスキップは自己署名証明書向け（https ノードのみ）。",
+      "tlsVerify": "検証（既定の CA）",
+      "tlsPin": "証明書をピン留め（SHA-256）",
+      "tlsSkip": "検証をスキップ",
+      "tlsSkipWarning": "検証をスキップすると中間者攻撃への保護がなくなり、API トークンが傍受される恐れがあります。証明書のピン留めを推奨します。",
+      "pinnedCert": "ピン留め証明書の SHA-256",
+      "pinnedCertHint": "ノード証明書の SHA-256（base64 または hex）。「取得」でノードから今すぐ読み取れます。",
+      "pinnedCertPlaceholder": "base64 または hex の SHA-256",
+      "fetchPin": "取得",
+      "pinFetched": "ノードの現在の証明書を取得しました",
+      "pinFetchFailed": "証明書を取得できませんでした"
     },
     "settings": {
       "title": "パネル設定",