adding-filters.md

Adding a Built-in AI Filter

Review the extensions guide first.

1. Create the filter module:
   • Provider API filters: apis/src/<provider>/
   • Cross-provider filters: filters/src/<category>/
2. Implement HttpFilter (from praxis-filter). Add a from_config factory that deserializes a serde_yaml::Value into your config struct.
3. Register it in praxis_ai_filters::register_ai_filters (in filters/src/register.rs).
4. Add unit tests and doctests.
5. Add an example config in the appropriate category under examples/configs/.
6. Add a functional integration test in tests/integration/tests/suite/.
7. Update examples/README.md to list any new or renamed example configs.

All testing requirements from CONTRIBUTING.md apply. A feature without tests and an example is not complete.