feat: add generic mcp-bridge for proxying upstream MCP SSE servers

- Add mcp-bridge/index.js: WebSocket backend for hub, relays requests
  to upstream MCP SSE servers via SSE+POST transport
- Add mcp-bridge/package.json with 'ws' dependency
- Add 'mcp-bridge-memory' entry to ecosystem.config.js (not started)
- Add 'bridge' script to root package.json
- Add mcp-bridge/node_modules to .gitignore

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

mcp-bridge/package-lock.json

@@ -0,0 +1,37 @@
+{
+  "name": "mcp-bridge",
+  "version": "1.0.0",
+  "lockfileVersion": 3,
+  "requires": true,
+  "packages": {
+    "": {
+      "name": "mcp-bridge",
+      "version": "1.0.0",
+      "license": "ISC",
+      "dependencies": {
+        "ws": "^8.19.0"
+      }
+    },
+    "node_modules/ws": {
+      "version": "8.19.0",
+      "resolved": "https://registry.npmjs.org/ws/-/ws-8.19.0.tgz",
+      "integrity": "sha512-blAT2mjOEIi0ZzruJfIhb3nps74PRWTCz1IjglWEEpQl5XS/UNama6u2/rjFkDDouqr4L67ry+1aGIALViWjDg==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=10.0.0"
+      },
+      "peerDependencies": {
+        "bufferutil": "^4.0.1",
+        "utf-8-validate": ">=5.0.2"
+      },
+      "peerDependenciesMeta": {
+        "bufferutil": {
+          "optional": true
+        },
+        "utf-8-validate": {
+          "optional": true
+        }
+      }
+    }
+  }
+}