docs: add Cursor Cloud dev environment instructions to AGENTS.md

[junior-tsai-god]

Note

This PR was AI-generated / AI-assisted (git user Cursor Agent, not a historical core developer).

📝 变更描述 / Description

Documents how to run the project in the Cursor Cloud dev environment by appending a ## Cursor Cloud specific instructions section to AGENTS.md. No application code is changed.

The section captures non-obvious, durable caveats discovered while setting up the environment:

• Dev run flow (backend go run main.go on :3000 with auto SQLite + optional Redis; web/default Rsbuild dev server on :5173 proxying /api, /mj, /pg).
• The //go:embed web/default/dist + web/classic/dist requirement — both dist dirs need an index.html for the backend to compile even in dev (placeholders mirror Dockerfile.dev).
• Fresh DB shows the setup wizard before login; make reset-setup resets it.
• The dev-only TanStack Router devtools panel can overlap dialog submit buttons during automated UI testing.
• bun run lint reports pre-existing errors unrelated to a given change.

🚀 变更类型 / Type of change

• 🐛 Bug 修复 (Bug fix)
• ✨ 新功能 (New feature)
• ⚡ 性能优化 / 重构 (Refactor)
• 📝 文档更新 (Documentation)

🔗 关联任务 / Related Issue

• N/A

✅ 提交前检查项 / Checklist

• 人工确认: 描述已整理撰写（本 PR 为 AI 辅助生成，已在上方标注）。
• 非重复提交: 仅新增文档说明。
• Bug fix 说明: 不适用。
• 变更理解: 已理解更改内容及影响（仅文档）。
• 范围聚焦: 仅改动 AGENTS.md。
• 本地验证: 后端、前端 dev server、lint、typecheck、Go 测试均已本地运行验证。
• 安全合规: 无敏感凭据。

📸 运行证明 / Proof of Work

Setup wizard on first launch (uninitialized system):
Setup wizard

Admin dashboard after login:
Dashboard after login

API key created (hello-world task):
Token created toast
Token list showing hello-world-token

_{To show artifacts inline, enable in settings.}