docs: clarify development constraints and error contracts

[AkashiSensei]

Clarify Crater development constraints and error-contract documentation across backend, frontend, CLI, website, and development Skills.

Changes

• Contributor docs: Refine root, backend, frontend, CLI, and website contribution guidance so development constraints are placed in the right authority documents instead of scattered across thin entrypoints.
• Backend/API errors: Document bizerr / resputil.HandleError expectations, point contributors to live definition files such as backend/internal/bizerr/groups.go, backend/internal/resputil/handle.go, and backend/internal/resputil/response.go, and keep concrete codes as examples rather than copied tables.
• Frontend and CLI error presentation: Clarify that clients should preserve actionable backend msg, HTTP status, and business-code facts while allowing frontend/CLI-specific presentation where needed.
• CLI constraints: Centralize admin namespace, argument validation, backend API support checks, Skill separation, error-context preservation, and common error-scenario recording in cli/docs/SPEC.md, cli/docs/REVIEW.md, CLI Skill templates, and shared CLI Skills.
• Development Skills: Update crater-devel-* Skills so future Agents route code/docs/review work consistently and prompt developers for the required manual checks.

Testing

AI:

• git diff --check: passed
• git commit -s: passed repository pre-commit hook, including Website, Frontend, and Backend checks
• diff -q between repository crater-devel-* Skills and locally installed ~/.agents/skills/crater-devel-*: matched after local sync
• Branch check: docs/issue-416-dev-constraints is 1 ahead / 0 behind relative to origin/main

Developer:

• Manually read all current modifications and confirmed the documentation and Skill changes are ready to submit.

Other

• This is a documentation and Skill-only change. No frontend UI behavior is changed, so screenshots are not included.

---

澄清 Crater 后端、前端、CLI、website 与开发 Skills 中的开发约束和错误返回契约。

修改

• 贡献文档：整理根目录、backend、frontend、CLI 和 website 的贡献说明，确保开发约束沉淀在合适的权威文档中，而不是分散在薄入口里。
• 后端 / API 错误：说明 bizerr / resputil.HandleError 的使用期望，指向 backend/internal/bizerr/groups.go、backend/internal/resputil/handle.go、backend/internal/resputil/response.go 等实时定义文件，并要求具体 code 只作为示例而不是复制成长表。
• 前端与 CLI 错误展示：明确客户端应保留后端 msg、HTTP 状态和业务码等排查事实，同时允许前端 / CLI 在需要时做本地化或领域化展示。
• CLI 约束：将管理员命名空间、参数校验、后端 API 支持检查、Skill 分离、错误 context 保留和常见报错场景沉淀规则集中到 cli/docs/SPEC.md、cli/docs/REVIEW.md、CLI Skill 模板和 shared Skill 中。
• 开发 Skills：更新 crater-devel-* Skills，让后续 Agent 在代码、文档和 review 任务中按同一套规则路由，并提示开发者完成必要人工检查。

测试

AI：

• git diff --check：通过
• git commit -s：通过仓库 pre-commit hook，包括 Website、Frontend 和 Backend checks
• diff -q 对比仓库内 crater-devel-* Skills 与本地安装的 ~/.agents/skills/crater-devel-*：本地同步后一致
• 分支检查：docs/issue-416-dev-constraints 相对 origin/main 为 1 ahead / 0 behind

开发者：

• 人工阅读检查了当前所有修改，并确认这些文档与 Skill 变更可以提交。

其他

• 本 PR 只修改文档和 Skills，不涉及前端 UI 行为，因此不附截图。

---

Resolve #416