Initialize harness coding docs from design spec

Split docs/softbox-catalog-design.md into the numbered harness doc set
(00-06, api.md, current-state, agent-context, tasks) following the
harness_coding_docs template and soft_quay conventions. Register the
nine open decision items from the design spec into the 06-tasks
roadmap as W- tasks and backlog entries. Keep the original design
spec as an archived design input with a header note.

Recreated after the repository's previous git history was lost to an
external reset; content matches the original initial commit.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/tasks/_template.md

@@ -0,0 +1,40 @@
+---
+id: W-XXX
+title: 一句话任务名
+phase: 1
+deps: []
+status: TODO
+created: 【日期】
+issue: null
+context_ref: null
+claim_branch: null
+work_branch: null
+write_paths:
+  - docs/tasks/W-XXX.md
+  - 【允许修改的仓库相对路径】
+---
+
+## 问题 / 背景
+
+(现象、根因、为什么要做)
+
+## 方案
+
+(怎么改,落到"改哪个文件、改成什么")
+
+## 验收要点
+
+(可验证的完成标准;按「passing 需证据」写清跑哪个验证命令,不写"应该能用"。裁定类任务写清结论落进哪个文档哪一节。)
+
+## 边界(不改什么)
+
+(明确不碰的模块/流程;涉及协议时重申:协议字段变更必须先走 soft_quay 客户端仓库)
+
+## 协作约束
+
+(领取时的 `context_ref`;任何新增写路径先检查与其他活跃任务是否重叠。)
+
+## 执行记录
+
+(做完在此记录:改了哪些文件、跑的验证命令与结果、阻塞、关键决策。
+执行记录只写进本任务文件,不逐任务追加共享的 `progress.md`。)