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).

frontend/src/pages/api-docs/endpoints.ts

@@ -769,6 +769,13 @@ export const sections: readonly Section[] = [
         body: '{\n  "scheme": "https",\n  "address": "node1.example.com",\n  "port": 2053,\n  "basePath": "/",\n  "apiToken": "abcdef..."\n}',
         response: '{\n  "success": true,\n  "obj": {\n    "status": "online",\n    "latencyMs": 42,\n    "xrayVersion": "25.x.x",\n    "panelVersion": "v3.x.x",\n    "cpuPct": 12.5,\n    "memPct": 45.2,\n    "uptimeSecs": 86400,\n    "error": ""\n  }\n}',
       },
+      {
+        method: 'POST',
+        path: '/panel/api/nodes/certFingerprint',
+        summary: "Connect to the node over HTTPS without verifying its certificate and return the leaf certificate's SHA-256 (base64). Used by the Add/Edit Node dialog to fetch and pin a self-signed certificate. Uses the same body as /test.",
+        body: '{\n  "scheme": "https",\n  "address": "node1.example.com",\n  "port": 2053,\n  "basePath": "/"\n}',
+        response: '{\n  "success": true,\n  "obj": "k3b1...base64-sha256...="\n}',
+      },
       {
         method: 'POST',
         path: '/panel/api/nodes/probe/:id',