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/nodes/NodesPage.tsx

@@ -30,7 +30,7 @@ export default function NodesPage() {
   useEffect(() => { setMessageInstance(messageApi); }, [messageApi]);
 
   const { nodes, loading, fetched, fetchError, refetch, totals } = useNodesQuery();
-  const { create, update, remove, setEnable, testConnection, probe, updatePanels } = useNodeMutations();
+  const { create, update, remove, setEnable, testConnection, fetchFingerprint, probe, updatePanels } = useNodeMutations();
 
   const { data: latestVersion = '' } = useQuery({
     queryKey: ['server', 'panelUpdateInfo'],
@@ -231,6 +231,7 @@ export default function NodesPage() {
           mode={formMode}
           node={formNode}
           testConnection={testConnection}
+          fetchFingerprint={fetchFingerprint}
           save={onSave}
           onOpenChange={setFormOpen}
         />