Preset/overlay system: org and project-level component customization

Summary

Add a preset/overlay system that lets organizations and projects customize PromptKit components (personas, protocols, formats, templates) without forking the core library — using a priority-based resolution stack.

Motivation

GitHub Spec Kit has a mature preset system with a clean design:

• Resolution stack: project overrides > org presets > extension templates > core templates
• Priority-based: Multiple presets stack with explicit priority ordering (lower number wins)
• Runtime resolution: Templates resolved dynamically on every lookup — presets can be added/removed without rebuilding
• Dual catalogs: Official (curated, install-allowed) + community (discoverable, explicit install)
• Scaffolding: Template directory for creating new presets

This solves a real PromptKit need. Today, organizations that want to:

• Replace systems-engineer with their own domain-specific persona
• Add company-specific guardrail protocols (""always use our internal auth library"")
• Customize the requirements-doc format with additional sections

...must either fork the repo or manually edit assembled output every time.

Proposed Design

PromptKit's ""code"" is all Markdown/YAML, so the preset system can be much simpler than Spec Kit's Python-based implementation:

1. Resolution stack for component lookup during assembly:

   Priority 1: .promptkit/overrides/{type}/{name}.md    (project-local)
   Priority 2: .promptkit/presets/{preset-id}/{type}/    (installed presets)
   Priority 3: {promptkit-repo}/{type}/{name}.md         (core library)
   

2. Preset manifest (preset.yaml):

   name: acme-corp-standards
   version: 1.0.0
   description: ACME Corp engineering standards overlay
   overrides:
     personas: [systems-engineer]
     protocols: [operational-constraints]
     formats: [requirements-doc]
   adds:
     protocols: [acme-security-review]
   

3. CLI support: npx promptkit preset add <path-or-url>

4. Catalog (future): A community catalog of preset packs for specific domains (embedded systems, web development, data engineering, etc.)

Credit

This pattern is directly inspired by GitHub Spec Kit's preset system. See their presets/ARCHITECTURE.md for the resolution stack design and presets/README.md for the CLI interface.

Start by locating the component lookup used during assembly and the CLI entry point for npx promptkit preset add <path-or-url>. Review the proposed preset.yaml manifest and the .promptkit/overrides and .promptkit/presets paths; done means priority-based resolution, preset installation, and project/org customization work without modifying core components.