feat(core): honor HTTPS_PROXY/HTTP_PROXY/NO_PROXY in the Node transport (closes #1563)

Wrap the Node transport's fetch with an undici EnvHttpProxyAgent dispatcher
when a standard proxy env var is set, so the CLI and web backend can reach
remote MCP servers through corporate proxies with zero new flags. undici is
imported lazily (only when a proxy var is present) and added as a dependency
at the repo root and in the CLI client; a missing undici raises an actionable
error. Documents the behavior and dependency in the CLI README.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S3fTN8H3R8YV4yUGvZjYnX

package-lock.json

@@ -26,6 +26,7 @@
         "open": "^10.2.0",
         "pino": "^9.14.0",
         "react": "^19.2.4",
+        "undici": "^8.5.0",
         "vite": "^8.0.0",
         "yaml": "^2.9.0",
         "zod": "^4.3.6",
@@ -3012,6 +3013,15 @@
         "node": ">= 0.6"
       }
     },
+    "node_modules/undici": {
+      "version": "8.5.0",
+      "resolved": "https://registry.npmjs.org/undici/-/undici-8.5.0.tgz",
+      "integrity": "sha512-xamtWoB1EshgjpmlXd7GGm2VfdDtw1+rD8uhry8pSNW3If6S8E0m2T2+orSKeZXEn/aPJMviCpDBA65WJt8zhg==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=22.19.0"
+      }
+    },
     "node_modules/unpipe": {
       "version": "1.0.0",
       "resolved": "https://registry.npmjs.org/unpipe/-/unpipe-1.0.0.tgz",