Add a minimal FastAPI example using AICertify

[kmadan]

Goal

Create examples/fastapi-app/ showing AICertify wrapped around a small FastAPI service: capture every /chat interaction into a contract and run an evaluation on demand via an admin endpoint.

Why this matters

FastAPI is one of the most common Python web frameworks. Showing AICertify next to a FastAPI app makes the 'this fits into my real stack' story concrete.

Files likely involved

• New: examples/fastapi-app/ following the six-file shape of the existing examples (see examples/customer-support-bot/ for the pattern)
• examples/README.md table entry
• The existing FastAPI dep is already in pyproject.toml

Acceptance criteria

• A runnable FastAPI service exposing a /chat endpoint and an /admin/evaluate endpoint
• Captured interactions persist to a contract JSON
• /admin/evaluate runs AICertify against the contract and returns the JSON report
• README documents how to run, what to send, and what to expect
• expected_report.md shows a sample run

Help

Comment here if you want to work on this and I will help you get started. First-time contributors are welcome — open a draft PR early and I'll review.