refactor(create-expert): document 4-level delegation depth architecture

[FL4TLiN3]

Summary

Add documentation explaining why the PBT framework uses a 4-level delegation structure.

Changes

Added Architecture Note to create-expert instruction explaining the separation of concerns:

## Architecture Note
The 4-level delegation depth (create-expert → integration-manager → functional/usability-manager → expert-tester)
is intentional for separation of concerns:
- Level 1: Orchestration (what to create)
- Level 2: Integration (coordinate testing types)
- Level 3: Stage management (functional vs usability)
- Level 4: Test execution (run and evaluate)

Rationale

Per user decision: documentation only, no design changes. The deep delegation chain exists because each level has a distinct responsibility:

1. create-expert: High-level orchestration of the PBT workflow
2. integration-manager: Coordinates functional and usability testing in parallel
3. functional/usability-manager: Manages specific test categories
4. expert-tester: Executes tests and evaluates results

This follows the principle of separation of concerns and allows each expert to focus on one thing.

Closes #358

🤖 Generated with Claude Code

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Note

Documents the intentional 4-level delegation structure within create-expert instructions; no functional logic changes.

• Updates create-expert-toml.ts with an Architecture Note clarifying roles: Level 1 (orchestration), Level 2 (integration), Level 3 (stage management), Level 4 (test execution)
• Adds .changeset/document-delegation-depth.md to release a patch note for create-expert

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Codecov Report

✅ All modified and coverable lines are covered by tests.

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