Extending FZGPUModules

Everything involved in adding a new stage.

Adding a stage

• How to Add a New Stage — the mechanical checklist for a stage that lives in this repository (files, StageType id, CMake, config, CLI, tests).
• Adding a stage outside the main repo — building a stage in your own repository against an installed FZGPUModules, without patching the library. Use this while a stage is unpublished or private; fold it back into How to Add a New Stage when it lands upstream.

Specialization

• Making a stage specialization-compatible — the declaration contract a stage implements to become eligible for Pipeline Specialization (fusion + finalize-time optimization).