docs: simplify the homepage and public repository layout

[nobodycareme]

Summary

• simplify the Chinese and English project homepages
• make the three primary getting-started paths explicit
• reorganize the bilingual documentation index without duplicate entries
• add structured GitHub community entry points and Issue Forms
• classify public tools without changing their existing paths

Design goals

• reduce repeated explanations
• keep the homepage focused on users rather than maintainers
• use concrete project-specific language
• preserve current URLs where practical
• keep v1.2.6 code, tags, and release assets unchanged

Validation

• python tools/check-doc-parity.py
• python tools/check-doc-links.py
• python tools/check-doc-language-links.py
• python tools/check-public-docs.py
• python tools/check-version.py
• python tools/check-readme-render.py
• python tools/security_scan.py
• python tools/test-public-docs-negative.py
• parsed all Issue Form and workflow YAML with PyYAML
• git diff --check

Scope

Documentation, community files, repository presentation, and their validation only. No firmware behavior, Cloud behavior, database, MQTT contract, PCB data, real IR data, version, tag, or Release asset changes.

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