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!

Start by reviewing the proposed /v1/query integration and the neuforge_pay meter_endpoint example, then inspect the repository's TypeScript MCP server entry points and request handling. Done would require an agreed approach for optional metering, paid API keys, token-cost calculation, and session budget enforcement, with the relevant tests identified before implementation.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.