Feature Suggestion: Optional token metering & paid API key support via `neuforge-pay`

Hi @getsentry,

Love the work on `getsentry/XcodeBuildMCP`! As usage grows across AI agent frameworks, server compute costs can start adding up quickly. We've also seen developers report that their autonomous agents accidentally burn through thousands of dollars in a single session because traditional payment rails lack built-in agent guardrails.

Would you be open to adding an optional usage metering & billing decorator using `neuforge-pay`? It acts as a proactive **Spend Firewall** and Merchant of Record for MCP servers. In 3 lines of code, it meters tokens, calculates live LLM COGS, and proactively blocks agent transactions that exceed a strict session budget limit (to prevent surprise bills).

Example Integration:
```python
from neuforge_pay import meter_endpoint

@app.get("/v1/query")
@meter_endpoint(price_charged_usd=0.05, model_name="claude-3-5-sonnet", session_budget_usd=10.00)
async def query_endpoint():
...
```

Happy to submit a clean PR if this aligns with your roadmap!

該 payload 沒有指出任何檔案、測試或進入點；請先定位 TypeScript MCP server 的 request 或 tool 註冊位置以及相依性設定。在實作之前，確認可選的 metering 和付費 API key 是否符合 roadmap，並定義受支援的計費邊界和預算行為；要視為完成，需要有 maintainer 核准的設計和測試。

由索引模型根據 Issue 內容生成。