Add github_search tool for discovering agent orchestration repos

[Copilot]

The Fat-Cat agent pipeline lacked a native way to search GitHub for repos — e.g., finding the latest agent-orchestration / multi-agent workflow projects. This adds a github_search tool that agents can invoke directly from Stage 4.

Changes

stage4_agent/tools_bridge.py

• New @tool-decorated github_search function using only Python stdlib (urllib) — no new dependencies
• Params: query (full GitHub search syntax supported), max_results (1–30), sort (stars/forks/updated/best-match), order (desc/asc)
• Auth: reads GITHUB_TOKEN or GH_TOKEN env var; falls back to anonymous (10 req/hr)
• Returns formatted output per repo: full name, URL, description, ⭐ stars, 🍴 forks, language, topics, last-updated date
• Gracefully handles HTTP errors, zero results, and network failures

tools/tool_catalog.md

• Documents github_search under 信息获取类 with params, use cases, output shape, and token note

test/test_github_search_tool.py

• 7 unit tests (all mocked): successful results, zero results, HTTP 403, max_results cap at 30, invalid sort fallback to stars, token header injection, registry registration

.gitignore

• Added to exclude __pycache__, *.pyc, .venv, dist/, etc.

Example usage

[TOOL_CALL]
tool: github_search
query: agent orchestration workflow topic:agent language:python
sort: stars
max_results: 10
[/TOOL_CALL]

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