refactor(iot): adopt reset-complete and centralized mqtt lifecycle

[shiliu-yang]

Align sample apps with SDK event flow; add secrets templates for cloud demos.

Made-with: Cursor

PR 描述/PR description

[在此详细描述 PR 的内容]/[Describe the PR content in detail here]

代码质量/Code Quality:

在本次拉取请求中，我已考虑以下事项 As part of this pull request, I've considered the following:

• 确保代码注释和文档清晰，并使用英文注释以保证代码可读性。Ensure that the code comments and documentation are clear, and use English for comments to ensure code readability.
• 确保文件头遵循文件头格式。Ensure that the file header follows the File Header Format.
• 确保函数头遵循 Doxygen 格式。Ensure that function headers follow the Doxygen format as specified in Comments.
• 已查阅 编码风格指南，并核查代码风格合规性，包括缩进、空格、命名规范及其他风格要求。 Reviewed the Coding Style Guide and verified code style compliance, including indentation, spacing, naming conventions, and other style guidelines.
• 已使用代码格式化工具确保符合 TuyaOpen 编码规范。Have used the code-formatting source code formatting tool to ensure compliance with TuyaOpen coding standards.

[shiliu-yang]

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Code review

No issues found. Checked for bugs and CLAUDE.md compliance. (Repository has no CLAUDE.md; AGENTS.md does not prescribe these event-flow details.)

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