feat(robomp): added repo-scoped issue search to issue triage flow

- Added `search_issues` support to the GitHub backend and client, including `state_reason` and `is_pull_request` in issue summaries.
- Added the `gh_search_issues` host tool with repo-prefixed query handling, non-empty/restricted `repo:` validation, default and bounded `limit` values, and inbound issue filtering.
- Added proxy integration for issue search with a new `/gh/v1/search_issues` endpoint and matching proxy-client method/response parsing.
- Updated triage prompts to perform pre-`classify_issue` duplicate and already-fixed checks via search, and added tests for search query formatting, validation, and state-aware match rendering.

python/robomp/tests/test_proxy_client.py

@@ -251,6 +251,29 @@ def round_trip_app(proxy_settings: Settings):
                     }
                 ],
             )
+        if path == "/search/issues" and req.method == "GET":
+            assert req.url.params["q"].startswith("repo:octo/widget ")
+            return httpx.Response(
+                200,
+                json={
+                    "total_count": 1,
+                    "items": [
+                        {
+                            "number": 9,
+                            "title": "fixed it",
+                            "state": "closed",
+                            "state_reason": "completed",
+                            "user": {"login": "bob"},
+                            "labels": [{"name": "bug"}],
+                            "comments": 2,
+                            "updated_at": "2026-02-01T00:00:00Z",
+                            "created_at": "2026-01-15T00:00:00Z",
+                            "html_url": "https://example/9",
+                            "pull_request": {"url": "https://example/pull/9"},
+                        }
+                    ],
+                },
+            )
         if path == "/repos/octo/widget/issues/1/comments" and req.method == "GET":
             return httpx.Response(
                 200,
@@ -365,6 +388,10 @@ async def test_round_trip_all_endpoints(round_trip_app) -> None:
     issues = await client.list_issues("octo/widget")
     assert len(issues) == 1 and isinstance(issues[0], IssueSummary)
 
+    found = await client.search_issues("octo/widget", "colon selector is:pr")
+    assert len(found) == 1 and isinstance(found[0], IssueSummary)
+    assert found[0].is_pull_request and found[0].state_reason == "completed"
+
     comments = await client.list_comments("octo/widget", 1)
     assert len(comments) == 1 and isinstance(comments[0], CommentInfo)