security: add nginx headers and fix npm vulnerabilities

- Add security headers to nginx (X-Frame-Options, CSP, etc.)
- Reduce client_max_body_size from 500M to 10M
- Add npm overrides to fix cookie vulnerability in csurf
- Make navbar sticky with full width

backend/package-lock.json

@@ -3437,15 +3437,6 @@
         "node": ">= 0.8.0"
       }
     },
-    "node_modules/csurf/node_modules/cookie": {
-      "version": "0.4.0",
-      "resolved": "https://registry.npmjs.org/cookie/-/cookie-0.4.0.tgz",
-      "integrity": "sha512-+Hp8fLp57wnUSt0tY0tHEXh4voZRDnoIrZPqlo3DPiI4y9lwg/jqx+1Om94/W6ZaPDOUbnjOt/99w66zk+l1Xg==",
-      "license": "MIT",
-      "engines": {
-        "node": ">= 0.6"
-      }
-    },
     "node_modules/csurf/node_modules/depd": {
       "version": "1.1.2",
       "resolved": "https://registry.npmjs.org/depd/-/depd-1.1.2.tgz",
@@ -5369,9 +5360,9 @@
       "license": "MIT"
     },
     "node_modules/js-yaml": {
-      "version": "3.14.1",
-      "resolved": "https://registry.npmjs.org/js-yaml/-/js-yaml-3.14.1.tgz",
-      "integrity": "sha512-okMH7OXXJ7YrN9Ok3/SXrnu4iX9yOk+25nqX4imS2npuvTYDmo/QEZoqwZkYaIDk3jVvBOTOIEgEhaLOynBS9g==",
+      "version": "3.14.2",
+      "resolved": "https://registry.npmjs.org/js-yaml/-/js-yaml-3.14.2.tgz",
+      "integrity": "sha512-PMSmkqxr106Xa156c2M265Z+FTrPl+oxd/rgOQy2tijQeK5TxQ43psO1ZCwhVOSdnn+RzkzlRz/eY4BgJBYVpg==",
       "dev": true,
       "license": "MIT",
       "dependencies": {