Add runnable examples (start with bulk-adding suppliers) #4

Runnable examples are a low-friction way to show what the SDK can do — copy, set two env vars, run. Let's grow an examples/ folder, starting with the most common first task: getting suppliers into the register fast.

First example: add_suppliers.py — define a list of suppliers (name, type, criticality, data access, CIA classification, markdown notes) and loop client.suppliers.add(...), printing the assigned identifier + CIA for each.

Also lint examples/ in CI (ruff check … examples) so a published example can't silently rot when the SDK changes.