feat(issue): add attachment read downloads (#218)

- Add a read-only `attachment_read` tool for issue and issue comment attachments.
- Use the existing Gitea SDK attachment metadata APIs for `list` and `get`.
- Add authenticated `/attachments/{uuid}` downloads in the MCP server for `download`, with small image inline results and streamed file downloads for larger content.
- Add `-max-inline-attachment-bytes` / `GITEA_MAX_INLINE_ATTACHMENT_BYTES` to configure inline image limits.
- Update the tool tables in all README variants.

Refs: #209

Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/218
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: yp05327 <576951401@qq.com>

README.zh-tw.md

@@ -151,6 +151,7 @@ Cursor 等客戶端可使用 stdio 命令：
 | package_read                 | 軟體套件 | 讀取 | 讀取軟體套件註冊表：列出套件、列出版本或取得某個版本                 |
 | package_write                | 軟體套件 | 寫入 | 刪除軟體套件版本（不可復原）                                         |
 | list_issues                  | 問題     | 讀取 | 列出倉庫問題                                                         |
+| attachment_read              | 問題     | 讀取 | 讀取問題/評論附件：列出中繼資料、取得中繼資料或下載內容             |
 | issue_read                   | 問題     | 讀取 | 讀取問題：詳情、評論或標籤                                           |
 | issue_write                  | 問題     | 寫入 | 寫入問題：創建、更新、管理評論和標籤                                 |
 | list_pull_requests           | 拉取請求 | 讀取 | 列出倉庫拉取請求                                                     |