docs: move engineering.md from docs/dev/ to planning/

The engineering doc is a planning/architecture reference (alongside
specs/, plans/, deferred-work.md), not user-facing documentation in
docs/. Move it under planning/ and update the live references in
CLAUDE.md and the v0.2 spec.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: lesnik512

CLAUDE.md

@@ -8,7 +8,7 @@ Guidance for AI agents (Claude Code, etc.) working in this repository.
 
 **Where to find what:**
 
-- [`docs/dev/engineering.md`](docs/dev/engineering.md) — the distilled design reference: invariants and *why*, the three protocol seams, exception contract, module layout, testing patterns, optional-extras pattern, remaining roadmap. Read this before adding any new module or extension point.
+- [`planning/engineering.md`](planning/engineering.md) — the distilled design reference: invariants and *why*, the three protocol seams, exception contract, module layout, testing patterns, optional-extras pattern, remaining roadmap. Read this before adding any new module or extension point.
 - [`planning/deferred-work.md`](planning/deferred-work.md) — review-surfaced items that are real but not actionable now.
 - [`planning/specs/`](planning/specs/) and [`planning/plans/`](planning/plans/) — per-feature design specs and implementation plans (active work).
 
@@ -89,5 +89,5 @@ Three documented internal boundaries. AI agents must respect them — never cros
 
 ## When in doubt
 
-- Check [`docs/dev/engineering.md`](docs/dev/engineering.md) before adding a new module or extension point.
+- Check [`planning/engineering.md`](planning/engineering.md) before adding a new module or extension point.
 - Surface ambiguity as a documentation gap rather than improvising.

docs/dev/engineering.md planning/engineering.mddocs/dev/engineering.md renamed to planning/engineering.md

@@ -3,7 +3,7 @@
 **Status:** spec — awaiting review
 **Author:** Artur Shiriev (with Claude)
 **Date:** 2026-06-03
-**Supersedes:** the 0.1.0 architecture documented in `docs/dev/engineering.md` (sections 2, 3, 5, 8)
+**Supersedes:** the 0.1.0 architecture documented in `planning/engineering.md` (sections 2, 3, 5, 8) — formerly at `docs/dev/engineering.md`, moved to `planning/` as part of this pivot
 
 ## 1. Intent