docs(plugin): keep one OpenCode plugin

[ZaynJarvis]

Summary

• remove the older split OpenCode plugin examples under examples/opencode-memory-plugin and examples/opencode/plugin
• keep examples/opencode-plugin as the only maintained OpenCode plugin example
• update OpenCode integration docs, agent gallery metadata, and basic usage links to point at the unified plugin
• expand OpenCode plugin installation guidance in English and Chinese docs with prerequisites, package/source install paths, configuration, verification, runtime logs, and troubleshooting

Validation

• npm run check in examples/opencode-plugin
• parsed docs/images/agents/{en,zh}/index.json with Node
• npm run docs:build in docs
• git diff --check

Note: npm ci in docs reported 3 existing moderate npm audit findings; no dependency changes were made.

[github-actions]

PR Reviewer Guide 🔍

Here are some key observations to aid the review process:

⏱️ Estimated effort to review: 1 🔵⚪⚪⚪⚪

🏅 Score: 95

🧪 No relevant tests

🔒 No security concerns identified

✅ No TODO sections

🔀 No multiple PR themes

⚡ Recommended focus areas for review Documentation Consistency Japanese agent integrations page was not updated to reflect the unified OpenCode plugin, while English and Chinese versions were. Documentation Consistency Japanese agent gallery metadata was not updated to reflect the unified OpenCode plugin, while English and Chinese versions were. Documentation Consistency Japanese OpenCode agent detail page was not updated to reflect the unified OpenCode plugin, while English and Chinese versions were.

[github-actions]

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