Example: L402-paywalled API endpoints for testing

Great work on the L402 tool support. I run a couple of live L402 endpoints that could be useful as integration examples or for testing the L402 flow:

**Text Generation** (21 sats/query)
```bash
# Step 1: Get invoice
curl -X POST https://maximumsats.com/api/dvm \
-H "Content-Type: application/json" \
-d '{"prompt": "Explain the Lightning Network in one sentence"}'
# Returns 402 + Lightning invoice

# Step 2: Pay invoice, then retry with payment hash
curl -X POST https://maximumsats.com/api/dvm \
-H "Content-Type: application/json" \
-H "Authorization: L402 " \
-d '{"prompt": "Explain the Lightning Network in one sentence"}'
```

**Image Generation** (100 sats/image)
```
POST https://maximumsats.com/api/imagegen
```

**Stats/Metadata**
```
GET https://maximumsats.com/stats
```

Stack: Cloudflare Workers + LNbits + Groq (Llama 3.3 70B) / Workers AI (FLUX.1 Schnell). Standard L402 flow with Lightning invoices.

Happy to adapt the flow if there's a specific L402 format the MCP server expects, or help document the integration in the README.