Rename spec 037-undo-redo to 006-undo-redo for sequential numbering

Delete merged feature branches (005–037) that inflated the auto-increment
counter in create-new-feature.sh, and renumber the undo-redo spec to
follow the existing 001–005 sequence.

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

specs/006-undo-redo/data-model.md

@@ -1,6 +1,6 @@
 # Data Model: Undo/Redo
 
-**Feature**: 037-undo-redo
+**Feature**: 006-undo-redo
 **Date**: 2026-03-26
 
 ## Entities

specs/006-undo-redo/plan.md

@@ -1,7 +1,7 @@
 # Implementation Plan: Undo/Redo
 
-**Branch**: `037-undo-redo` | **Date**: 2026-03-26 | **Spec**: [spec.md](spec.md)
-**Input**: Feature specification from `/specs/037-undo-redo/spec.md`
+**Branch**: `006-undo-redo` | **Date**: 2026-03-26 | **Spec**: [spec.md](spec.md)
+**Input**: Feature specification from `/specs/006-undo-redo/spec.md`
 
 ## Summary
 
@@ -40,7 +40,7 @@ Add undo/redo capability for all encounter state changes using the memento patte
 ### Documentation (this feature)
 
 ```text
-specs/037-undo-redo/
+specs/006-undo-redo/
 ├── plan.md              # This file
 ├── research.md          # Phase 0 output
 ├── data-model.md        # Phase 1 output

specs/006-undo-redo/quickstart.md

@@ -1,6 +1,6 @@
 # Quickstart: Undo/Redo
 
-**Feature**: 037-undo-redo
+**Feature**: 006-undo-redo
 **Date**: 2026-03-26
 
 ## Overview

specs/006-undo-redo/research.md

@@ -1,6 +1,6 @@
 # Research: Undo/Redo for Encounter Actions
 
-**Feature**: 037-undo-redo
+**Feature**: 006-undo-redo
 **Date**: 2026-03-26
 
 ## Decision 1: Undo/Redo Strategy — Memento (Snapshots) vs Command (Events)

specs/006-undo-redo/spec.md

@@ -1,6 +1,6 @@
 # Feature Specification: Undo/Redo
 
-**Feature Branch**: `037-undo-redo`
+**Feature Branch**: `006-undo-redo`
 **Created**: 2026-03-26
 **Status**: Draft
 **Input**: Gitea issue #16 — Undo/redo for encounter actions

specs/006-undo-redo/tasks.md

@@ -1,6 +1,6 @@
 # Tasks: Undo/Redo
 
-**Input**: Design documents from `/specs/037-undo-redo/`
+**Input**: Design documents from `/specs/006-undo-redo/`
 **Prerequisites**: plan.md, spec.md, research.md, data-model.md, quickstart.md
 
 **Tests**: Domain tests included (pure function testing is standard for this project per CLAUDE.md).