docs(readme): example count 6 → 7

The per_product_policy_merchant.py example was added but the count line wasn't updated.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: vvillait88

README.md

@@ -292,7 +292,7 @@ async def purchase(request: Request):
 
 ## Examples
 
-The [examples/](./examples) directory has 6 runnable single-file FastAPI apps covering common merchant scenarios. See [examples/README.md](./examples/README.md) for the full table.
+The [examples/](./examples) directory has 7 runnable single-file FastAPI apps covering common merchant scenarios. See [examples/README.md](./examples/README.md) for the full table.
 
 ## Stability