Modularize web-search-agent with strategy modules

Split inline search strategies into separate module files (github-debug,
general-web, academic-papers, chinese-tech, stackoverflow). Agent now
loads modules dynamically via Read tool before searching. Update install
instructions to include module files.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

agents/web-search-modules/github-debug.md

@@ -0,0 +1,18 @@
+# GitHub Debug Module
+
+> 从 web-search-agent.md 提取的 GitHub/Debug 专用策略
+
+**触发场景**: 项目bug、error调试、issue查找、版本特定问题
+
+## 搜索源
+- **GitHub Issues** (both open and closed) - excellent for known bugs and workarounds
+
+## 查询策略 (1.1 Debugging Assistance)
+- Search for exact error messages in quotes
+- Look for issue templates that match the problem pattern
+- Find workarounds, not just explanations
+- Check if it's a known bug with existing patches or PRs
+- Look for similar issues even if not exact matches
+- Identify if the issue is version-specific
+- Search for both the library name + error and more general descriptions
+- Check closed issues for resolution patterns