feat(robomp): added local issue indexing and commit-search tool support

- Added `ROBOMP_ISSUE_INDEX_SYNC_SECONDS` configuration and lifecycle-managed issue indexing through startup/shutdown hooks.
- Added issue/PR index tables with FTS5 triggers plus upsert and keyword/filter search helpers for indexed records.
- Added GitHub backend/proxy support for `IssueIndexEntry` and issue-index page retrieval, including webhook ingestion and periodic watermark-driven sync.
- Updated `gh_search_issues` to prefer local index queries when synchronized and added `search_commits` host tool with query modes and validation.

python/robomp/src/proxy_client.py

@@ -25,6 +25,7 @@ from robomp.git_ops import GitCommandError, HeadDriftError, PushResult
 from robomp.github_client import (
     CommentInfo,
     GitHubError,
+    IssueIndexEntry,
     IssueInfo,
     IssueSummary,
     PullRequestFileInfo,
@@ -212,6 +213,20 @@ class GitHubProxyClient:
         )
         return [_issue_summary_from(item) for item in (data.get("items") if isinstance(data, dict) else None) or []]
 
+    async def list_issue_index_entries(
+        self,
+        repo: str,
+        *,
+        since: str | None = None,
+        page: int = 1,
+        per_page: int = 100,
+    ) -> list[IssueIndexEntry]:
+        params: dict[str, Any] = {"repo": repo, "page": page, "per_page": per_page}
+        if since:
+            params["since"] = since
+        data = await self._request("GET", "/gh/v1/issue_index_entries", params=params)
+        return [_index_entry_from(item) for item in (data.get("items") if isinstance(data, dict) else None) or []]
+
     async def list_comments(self, repo: str, number: int) -> list[CommentInfo]:
         data = await self._request("GET", "/gh/v1/comments", params={"repo": repo, "number": number})
         return [_comment_from(item) for item in (data.get("items") if isinstance(data, dict) else None) or []]
@@ -511,6 +526,27 @@ def _issue_summary_from(data: Any) -> IssueSummary:
     )
 
 
+def _index_entry_from(data: Any) -> IssueIndexEntry:
+    if not isinstance(data, dict):
+        raise GitHubError(500, "proxy returned malformed issue index payload")
+    return IssueIndexEntry(
+        repo=str(data["repo"]),
+        number=int(data["number"]),
+        is_pull_request=bool(data.get("is_pull_request")),
+        title=str(data.get("title") or ""),
+        body=str(data.get("body") or ""),
+        state=str(data.get("state") or ""),
+        state_reason=str(data.get("state_reason") or ""),
+        merged_at=str(data.get("merged_at") or ""),
+        author=str(data.get("author") or ""),
+        labels=tuple(str(x) for x in (data.get("labels") or [])),
+        comments=int(data.get("comments") or 0),
+        created_at=str(data.get("created_at") or ""),
+        updated_at=str(data.get("updated_at") or ""),
+        html_url=str(data.get("html_url") or ""),
+    )
+
+
 def _comment_from(data: Any) -> CommentInfo:
     if not isinstance(data, dict):
         raise GitHubError(500, "proxy returned malformed comment payload")