Implement registry scaffolding for profiles, gateways, providers, skills, and runners

[wauputr4]

Goal

Add explicit registries so new profiles, gateways, providers, skills, and runners can be added without editing core workflow logic.

Scope

• Add registry scaffolding for profiles.
• Add registry scaffolding for customer gateways and owner gateways.
• Add registry scaffolding for OpenAI-compatible providers.
• Add registry scaffolding for skills.
• Add registry scaffolding for orchestration runners.

References

• docs/22-architecture-boundaries.md
• docs/17-profile-template.md
• docs/21-skills-and-execution.md

Acceptance Criteria

• startup_saas can register as a profile.
• webhook can register as both customer and owner gateway type.
• openai-compatible can register as provider type.
• MVP-safe skills can register without hardcoded branching in the workflow.
• Registries are simple and local-first for MVP.