Add harness coding docs for SoftBox (Go + Gio dual-build)

Initialize the full harness coding document set from the
harness_coding_docs template, customized for the SoftBox project:

- Vision, requirements, tech stack (modern Go 1.25 + Gio v0.10.1;
  Win7 legacy Go 1.20.14 + Gio v0.6.0), architecture, coding rules
- Protocol contracts (signed catalog, package protocol v1, Ed25519
  license, events, CLI) and Gio view structure
- Roadmap Phase 0-6 with 20 suggested tasks; T-001 (monorepo
  skeleton) filed and ready to claim
- Agent entry points (AGENTS.md, docs/00-ai-start-here.md),
  context manifest, governance scripts and tests
- Merge Go gitignore with harness rules; keep go.work tracked

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

.gitea/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,33 @@
+## 任务映射
+
+- Closes #【Issue 编号】
+- task_file: `docs/tasks/T-XXX.md`
+- context_ref: `【领取任务时的提交 SHA】`
+- claim_branch: `claims/T-XXX`
+- work_branch: `agent/【agent-id】/T-XXX`
+- write_paths:
+  - `docs/tasks/T-XXX.md`
+  - `【本 PR 允许修改的仓库相对路径】`
+
+## 变更摘要
+
+【改了什么，以及为什么符合任务方案。】
+
+## 验证证据
+
+| 命令 | 结果 |
+| --- | --- |
+| `【真实命令】` | 【通过 / 失败摘要】 |
+
+## 风险与回滚
+
+【已知风险、兼容性影响、回滚方法；没有则写“无”。】
+
+## 检查清单
+
+- [ ] 当前 PR 只对应一个任务 / Issue。
+- [ ] 变更未超出 `write_paths`，没有夹带无关修改。
+- [ ] 任务文件执行记录包含相同的验证证据。
+- [ ] 合并前任务文件 frontmatter 已为 `DONE`；`Closes` 自动关闭 Issue 不会制造假完成。
+- [ ] 未提交 Token、Authorization header、私有配置或实例地址。
+- [ ] Issue 已切换到唯一 `status/review`；合并后才标记 `status/done`。