docs: promote develop to main

[kovawx]

Summary

Promote the current develop documentation snapshot to main for the next stable docs release.

Included changes

• add the ZeroDeNet community entry points and GitHub Discussions integration
• add structured Discussion Forms for Q&A, Ideas, and Development
• make README.md English and preserve the Chinese version as README.zh-CN.md
• expand Zboard deployment, node, protocol, subscription, DNS/certificate, troubleshooting, and contribution documentation
• update Zero Core protocol, proxy/URLTest, compatibility, and breaking-change documentation
• update ZNet Sink subscription, proxy/probe, diagnostics, feature, and troubleshooting documentation
• add use-case navigation and refine project/community navigation
• include repository metadata and documentation maintenance updates accumulated on develop

Branch status

• source: develop
• target: main
• develop is 34 commits ahead of main
• develop is 0 commits behind main

Validation

This PR promotes the already reviewed develop snapshot. GitHub Actions should run the standard documentation validation and production build before merge.

After merge, Discussion Category Forms under .github/DISCUSSION_TEMPLATE/ will become active because main is the repository default branch.