fix: address Copilot review follow-ups from #56; docs: add n8n integration guide

[KochC]

Summary

Addresses all four review comments left by copilot-pull-request-reviewer on #56, plus documents the n8n integration use case in the README.

Review follow-ups

1. knownToolIDs grows unbounded (real issue): replaced the ever-growing Set with slotToolIDs, a Map keyed by slot name whose entries are replaced (not accumulated) every time that slot is reused. Bounded by pool size regardless of how many requests / unique tool schemas a long-lived process handles over its lifetime, instead of growing forever and bloating every subsequent turn's tools payload.
2. Slot leak if registerToolBridge() throws after acquiring a slot (real issue, more serious): now releases its acquired slot back to the pool if anything after acquisition throws (e.g. client.mcp.add() failing to spawn/register the bridge). Previously such a slot was lost forever, since runAgentTurn() only releases a bridge once registerToolBridge() has already returned successfully — repeated failures would eventually exhaust the whole pool and hang every future tool-calling request in acquireBridgeSlot().
3. Test leaks bridge slots without cleanup: the slot-isolation test now releases both bridges it acquires via releaseToolBridge() (now exported) in an after() hook instead of leaking them into the shared global pool for the rest of the test process.
4. Second test doesn't reset global state: added general hygiene here too (see new regression test below), though the specific buildToolsMap(baseTools, null) case doesn't actually touch global state at all in this implementation (it returns early before calling getToolBridgeState()).

Also added a new regression test specifically for #2 (the slot-leak-on-failure fix): repeats a failing registration well beyond the pool size and confirms a subsequent registration still succeeds promptly, wrapped in a timeout race since node:test has no default per-test timeout and a regression would otherwise hang the suite instead of failing it cleanly.

Docs

README.md now documents using the proxy to pipe OpenCode's authenticated providers (GitHub Copilot, Anthropic, Bedrock, local Ollama, etc.) into n8n's native AI nodes — credential setup for both OpenAI/Anthropic node types, the model picker auto-populating from GET /v1/models, Basic LLM Chain vs. AI Agent + Tools, and the Docker-on-a-different-host + firewall caveat (learned the hard way testing this for real).

Testing

• npm test — 141 passed (140 + 1 new)
• npm run lint — clean

Related

• Follow-up to fix: disable stale bridge tool IDs from other pool slots #56 (review comments left by Copilot)