Tool: github_search (#38)

* Tool: searxng_search

Add searxng_search tool sources and focused docs from develop, sliced as an independent feature. Based on main for minimal diff; marked draft pending scaffold merge.

* Tool: pdf_extract

Add pdf_extract tool sources and docs from develop as an independent feature.

* Tool: wiki_query

Add wiki_query tool sources from develop as an independent feature.

* Tool: openalex_search

Add openalex_search tool sources and docs from develop as an independent feature.

* Tool: crossref_search

Add crossref_search tool sources and docs from develop as an independent feature.

* Tool: github_search

Add github_search tool sources and docs from develop as an independent feature.

---------

Co-authored-by: aibuddy <aibuddy@dev.hg.fi>

Author: heusalagroupbot

docs/reference/github_search.md

@@ -0,0 +1,12 @@
+### github_search
+
+- stdin: `{ "q": string, "type": "repositories|code|issues|commits", "per_page?": 10 }`
+- stdout: `{ "results": [ ...minimal per type... ], "rate": { "remaining": int, "reset": int } }`
+- env: optional `GITHUB_TOKEN`
+- behavior: uses `Accept: application/vnd.github+json`, 8s timeout (override via `HTTP_TIMEOUT_MS`), 1 retry on 5xx, SSRF guard blocks private/loopback.
+- rate limit: if `X-RateLimit-Remaining` is `0`, exits non-zero with stderr JSON: `{"error":"RATE_LIMITED","hint":"use GITHUB_TOKEN"}`.
+
+Example (repositories):
+```bash
+echo '{"q":"language:go stars:>5000","type":"repositories"}' | ./tools/bin/github_search | jq '.results[0]'
+```