fix: Distributed API auth hardening — Bearer tokens and URL normalization

- Extend WS upgrade handler to accept Authorization: Bearer tokens as a
  fallback to cookie auth. Remote Sencho instances receive proxied WS
  connections carrying Bearer (no cookie), so the previous cookie-only
  check caused immediate 401 rejections for all proxied log/terminal streams.
- Log token validation failures in authMiddleware (was silently swallowed,
  violating no-empty-catch directive).
- Normalize api_url by stripping trailing slashes in testRemoteConnection,
  the HTTP proxy target, and the WS proxy target to prevent double-slash URLs.

backend/src/services/NodeRegistry.ts

@@ -154,7 +154,8 @@ export class NodeRegistry {
         }
 
         try {
-            const response = await axios.get(`${node.api_url}/api/auth/check`, {
+            const baseUrl = node.api_url.replace(/\/$/, '');
+            const response = await axios.get(`${baseUrl}/api/auth/check`, {
                 headers: { Authorization: `Bearer ${node.api_token}` },
                 timeout: 8000,
             });