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

clients/cli/package.json

@@ -38,6 +38,7 @@
     "atomically": "^2.1.1",
     "commander": "^13.1.0",
     "pino": "^9.14.0",
+    "undici": "^8.5.0",
     "zod": "^4.3.6",
     "zustand": "^5.0.13"
   },