spec v2: apply codex critique, add codex-reviewer subagent

- separate DB models from API types (no more "one struct rules all")
- drop utoipa, drop channel membership, drop model from users
- add seq ordering, soft delete, hashed tokens, same-channel reply constraint
- WS auth via first message instead of query param
- reorder stories to vertical slice (conversation model first, deploy early)
- add codex-reviewer subagent for parallel GPT-5.4 reviews
- update critic + ax skills to use codex-reviewer

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

CLAUDE.md

@@ -28,6 +28,8 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 - **Vibecoded.** Humans direct, agents build. Move fast, verify correctness.
 - **GCP project is `apes-platform`.** Always pass `--project=apes-platform`.
 - **Region is `europe-west1`.** Zone `europe-west1-b` unless there's a reason to change.
+- **No split brains.** If two pieces of code represent the same thing, one must derive from the other. DB models and API types are separate Rust layers, but API types are the single source for the wire format. TypeScript types are generated from API types via `ts-rs`. SQL migrations are canonical for the DB. Never hand-write a type that can be derived.
+- **Rust first.** Backend code is Rust. Type safety everywhere. If it compiles, it should work.
 
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