Prevent Margin Leaks & Surprise LLM Bills: Add a Hybrid Spend Firewall

Hi @dair-ai,

Love the work on `dair-ai/Prompt-Engineering-Guide`! As you transition from open-source into commercializing your AI agent, you'll likely run into a major scaling problem: **power users running infinite loops and bankrupting your LLM budget.**

Currently, most frameworks require you to pay the Anthropic/OpenAI bill out of pocket or build a complex Stripe billing backend from scratch.

We built **NeuForge Pay**, a 5-line Python SDK that acts as a proactive Spend Firewall and Hybrid Merchant of Record. It blocks transactions *before* inference runs if the user exceeds their session budget, and lets them instantly top-up via **Stripe (Credit Card)** or **Coinbase Commerce (USDC on Base for M2M Agent payments)**.

**You can test how fast unmetered agents destroy margins using our interactive calculator here:**
[NeuForge AI Margin Leak Calculator](https://neuforge.app)

**Example Integration:**
```python
from neuforge_pay import meter_endpoint, neuforge_stripe_webhook, neuforge_coinbase_webhook

# Mount BOTH Fiat and Crypto webhooks
app.include_router(neuforge_stripe_webhook)
app.include_router(neuforge_coinbase_webhook)

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

If you are looking to monetize this project without getting burned by unpredictable LLM usage, we'd love for you to try it out!

The issue proposes integrating an external Python SDK with Stripe and Coinbase Commerce, but it names no repository files, tests, or entry points. First establish whether this project wants a spend-firewall integration at all; no acceptance criteria or definition of done is provided.

Written by the indexing model from the issue text.