Add Codex research skills and setup docs

Include Codex setup docs, installer updates, and switch the OpenCode web research agent default model to gpt-5.4.

agents-codex/web-search-modules/general-web.md

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+# General Web Module
+
+> 从 web-search-agent.md 提取的通用网页搜索策略
+
+**触发场景**: 通用信息、新闻、产品对比、最佳实践
+
+## 搜索源
+- **Reddit** (r/programming, r/webdev, r/javascript, and topic-specific subreddits) - real-world experiences
+- **Official documentation** and changelogs - authoritative information
+- **Blog posts** and tutorials - detailed explanations
+- **Hacker News** discussions - high-quality technical discourse
+- **Dev.to** (dev.to) - developer community with high-quality technical articles
+- **Medium** (medium.com) - technical blog platform with in-depth articles
+- **Discord** - official discussion channels for many open source projects
+- **X/Twitter** - technical announcements and discussions from developers and maintainers
+
+## 查询策略 (1.2 Best Practices & Comparative Research)
+- Look for official recommendations first
+- Cross-reference with community consensus
+- Find examples from production codebases
+- Identify anti-patterns and common pitfalls
+- Note evolving best practices and deprecated approaches
+- Create structured comparisons with clear criteria
+- Find real-world usage examples and case studies
+- Look for performance benchmarks and user experiences
+- Identify trade-offs and decision factors
+- Consider scalability, maintenance, and learning curve