chore: gitignore release/ 暂存目录（含上传用的重命名 EXE）

release/ 是上传到 Gitea release page 之前的暂存目录，canonical 产物在 Gitea（v0.1.0 资产 windows-gotify-client-rust-v0.1.0-x86_64-pc-windows-msvc.exe 已上传，download URL 在 LAN 上可达）。AGENTS.md §56 允许 release 里没二进制。

.gitignore

@@ -50,4 +50,12 @@ logs/
 
 # --- UPX / packing artifacts ---
 *.upx
-packed/
+packed/
+
+# --- Release staging ---
+# `release/` is a scratch dir we copy the built EXE into before
+# pushing it to Gitea's release page. We gitignore the whole dir
+# (including the *named* binaries) so we never accidentally commit
+# a 10 MB blob — the canonical artifact lives on Gitea, not in
+# the repo. (AGENTS.md §56 "可以接受 release 里没二进制".)
+/release/