feat: rewrite create-expert v2.0.0 — plan/write/verify with CLI validation

Architecture overhaul based on 100+ test runs:

- Plan restored as "context expansion" — maximizes context before authoring
- Write uses `perstack validate` and `perstack schema` CLI tools instead
  of LLM-based review (which was unreliable for structural correctness)
- Verify does test execution + ONE completion signal check (no separate
  test expert — context separation caused misunderstanding)
- Verify appends results to plan.md for cross-iteration knowledge continuity
- Review and test experts removed
- Completion signal: ONE, binary, deterministic, essential
- Max 3 iterations

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: FL4TLiN3

.changeset/validate-schema-create-expert-v2.md

@@ -0,0 +1,6 @@
+---
+"perstack": minor
+"@perstack/perstack-toml": minor
+---
+
+feat: add `perstack validate` and `perstack schema` CLI commands, rewrite create-expert v2.0.0