docs: clarify eager MCP proxy discovery

[poe-code-agent]

Summary

• Document that Toolcraft MCP proxy discovery is eager before CLI help/routing.
• Document that cached schemas avoid repeated upstream discovery and that selective/lazy proxy discovery is not currently supported.
• Make the memory cache malformed-JSON test tolerate Node JSON parse message location differences so the required push checks pass on this Node runtime.

Fixes #238

Verification

• npm run build
• npm run lint:types
• npm run test:unit -- packages/memory/src/cache.test.ts
• npm run test (via pre-push hook; 5919 passed, 1 skipped)

[poe-code-agent]

Requested changes: SDK proxy discovery timing is misstated.

[poe-code-agent]

LGTM