feat(connector): add search and fetch tools for ChatGPT connectors

Add a new "connector" domain exposing exactly-named "search" and "fetch"
MCP tools for ChatGPT-style connector compatibility (gitea#84). search
looks up repositories via the existing SearchRepos SDK call, optionally
resolving an owner/org name to an owner ID, and returns concise entries
(id, name, url, html_url). fetch reuses GetContents to read a file and
decodes its base64 content, returning path, sha, size, encoding and the
decoded content. Registers connector.Tool in operation.go and documents
the two tools in all three README tables.

Co-Authored-By: Codet <codet@commitgo.dev> (GPT-5-Codex)

README.zh-tw.md

@@ -191,6 +191,8 @@ Cursor 等客戶端可使用 stdio 命令：
 | get_release                  | release      | 讀取 | 依 ID 取得版本發布 |
 | get_latest_release           | release      | 讀取 | 取得最新版本發布 |
 | list_releases                | release      | 讀取 | 列出倉庫版本發布 |
+| search                       | connector    | 讀取 | 為 ChatGPT 風格的連接器依關鍵字搜尋 Gitea 倉庫 |
+| fetch                        | connector    | 讀取 | 為 ChatGPT 風格的連接器取得檔案的解碼內容與中繼資料 |
 
 > **說明：** 部分工具是聚合的、基於操作的工具，單個工具透過 `method` 參數暴露多個操作。當伺服器以唯讀模式執行時（`-r` / `GITEA_READONLY`），存取為「寫入」的工具會被隱藏；可透過 `-S` / `--scope`（`GITEA_SCOPES`）依範圍過濾，或透過 `-O` / `--tools`（`GITEA_TOOLS`）依工具名稱過濾對外暴露的工具集合。