feat: Documentation Updates for Persona Distribution

[katriendg]

Parent: #431

Issue Description

Update documentation to reflect the persona-based distribution model. Create per-collection descriptions and update contributing guidelines for persona tagging.

Motivation

Documentation must explain how to tag new artifacts, how collections work, and what each persona package contains. Contributors need clear guidance to maintain persona assignments as new artifacts are added.

Deliverables

1. Contributing Documentation Updates

Update docs/contributing/ files:

• custom-agents.md - Add guidance on selecting persona tags when creating agents
• instructions.md - Add persona tagging guidance for new instructions
• prompts.md - Add persona tagging guidance for new prompts
• skills.md - Add persona tagging guidance for new skills
• ai-artifacts-common.md - Add section on the artifact registry, persona taxonomy, and dependency declarations

2. Architecture Documentation Updates

Update docs/architecture/:

• ai-artifacts.md - Document the registry design, persona model, and collection build system
• Add collection/persona architecture section

3. Per-Collection Descriptions

Create description content for each collection package:

• Full collection README content
• Developer collection README content
• TPM collection README content
• DevOps collection README content
• Architect collection README content
• Technical Writer collection README content
• Used in Marketplace listing and extension README

4. Getting Started Updates

Update docs/getting-started/:

• install.md - Document persona selection during installation
• Method-specific docs - Note which methods support persona filtering

5. Extension Packaging Documentation

Update extension/PACKAGING.md:

• Document how to build persona-specific collection packages locally
• Inner developer loop: testing collection manifests and registry filtering
• Commands to build and validate individual collections (e.g., -Collection developer)
• How to verify artifact inclusion/exclusion for a collection
• Troubleshooting collection build issues

Acceptance Criteria

• Contributing docs explain persona tagging for each artifact type
• Architecture docs describe the registry design and collection model
• Each collection has a description suitable for Marketplace listing
• Getting started docs reflect the persona selection experience
• Persona taxonomy is documented consistently (developer, tpm, devops, architect, technical-writer)
• PACKAGING.md documents local testing workflow for collection builds

Additional Context

• Existing contributing docs: docs/contributing/
• Existing architecture docs: docs/architecture/
• Depends on: feat: AI Artifacts Registry Design and Schema #432 (Phase 1: Registry Design and Schema)
• Artifact categorization content comes from: Phase 6 (Persona-to-Artifact Mapping)

[katriendg]

Updating scope for collection-based architecture (PR #439, tracked in #519).

Most documentation deliverables here have been completed but re-scoped from persona-based to collection-based terminology:

• Architecture docs, contributing guides, PACKAGING.md, and getting started docs are updated for the collection model.
• Persona-specific deliverables (per-persona Marketplace descriptions, persona tagging guidance, persona taxonomy docs) are no longer relevant.

Remaining work re-scoped to collections:

• Per-collection descriptions suitable for Marketplace listing (10 domain collections instead of 5 personas)
• Verify all collection .collection.md companion files have adequate content