Docs: document Perstack Properties (PS-XXX) framework or internalize as create-expert-only concept

[FL4TLiN3]

Description

The create-expert framework defines "Perstack Properties" with PS-XXX identifiers, but these are not documented in the public documentation. This creates confusion about whether these are official Perstack concepts or internal implementation details.

Current State

In apps/create-expert/src/lib/create-expert-toml.ts:

### Perstack Properties (PS-XXX format)

**Security:**
- PS-SEC-01: Minimal tool access - uses `pick` for only needed tools
- PS-SEC-02: Minimal environment - uses `requiredEnv` for only needed variables
- PS-SEC-03: Maintains boundaries - protects internal information

**Design:**
- PS-DESIGN-01: Single responsibility - does one thing well
- PS-INST-01: Declarative instructions - policies not procedures
- PS-INST-02: Contains domain knowledge

**Output:**
- PS-OUT-01: Uses `attemptCompletion` for final output
- PS-OUT-02: Error handling - graceful with helpful messages

Also in apps/create-expert/src/lib/agents-md-template.ts (AGENTS.md template).

However, docs/making-experts/best-practices.md does not mention these identifiers. The "Five Principles" in docs are:

1. Do One Thing Well
2. Trust the LLM, Define Domain Knowledge
3. Let Them Collaborate
4. Keep It Verifiable
5. Ship Early

Questions to Resolve

1. Are PS-XXX properties meant to be public Perstack standards?

   • If yes: Document them in docs/making-experts/best-practices.md
   • If no: Rename to avoid confusion with official Perstack concepts

2. How do PS-XXX properties map to the Five Principles?

   • PS-DESIGN-01 ≈ Principle Docs: Add related documentation links to runtime README #1 (Do One Thing Well)
   • PS-INST-01, PS-INST-02 ≈ Principle chore: version packages #2 (Trust the LLM)
   • Others don't have clear mappings

Affected Areas

• apps/create-expert/src/lib/create-expert-toml.ts
• apps/create-expert/src/lib/agents-md-template.ts
• docs/making-experts/best-practices.md (if documenting)

Acceptance Criteria

Option A: Document PS-XXX publicly

• Add PS-XXX properties to docs/making-experts/best-practices.md
• Explain relationship to Five Principles
• Add reference in creating-expert workflow

Option B: Internalize as create-expert-only

• Rename to avoid "Perstack Properties" terminology
• Clarify in AGENTS.md that these are framework-specific
• Keep docs/best-practices.md as the public standard

[github-actions]

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