Remove Socket.IO dependencies and Socket infrastructure

- Remove socket.io-client npm package
- Remove Socket.IO from gulpfile.js
- Remove API_PUBLIC_WS_URL config variable from all environments
- Remove Socket CSP directives (cdn.socket.io, wss:// URLs)
- Remove unused data-host attribute from job template
- Update test_headers.py to remove Socket.IO assertions
- Update deployment configs (manifest.yml, deploy-config/*.yml, .github/workflows/*.yml)

gulpfile.js

@@ -81,8 +81,7 @@ const javascripts = () => {
     paths.npm + 'query-command-supported/dist/queryCommandSupported.min.js',
     paths.npm + 'textarea-caret/index.js',
     paths.npm + 'cbor-js/cbor.js',
-    paths.npm + 'd3/dist/d3.min.js',
-    paths.npm + 'socket.io-client/dist/socket.io.min.js'
+    paths.npm + 'd3/dist/d3.min.js'
   ]);
 
   // Concatenate all streams