feat: split git credential config by OS on Linux and macOS

Use includeIf so Linux prefers libsecret with cache fallback, while macOS keeps osxkeychain.

Co-authored-by: Cursor <cursoragent@cursor.com>

git/git-credential-linux.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+# Linux 凭据 helper：优先 libsecret，否则回退 cache 并提示安装
+set -euo pipefail
+
+warn_missing_libsecret() {
+    local marker="${XDG_CACHE_HOME:-$HOME/.cache}/git-credential-linux.warned"
+    [[ -f "$marker" ]] && return 0
+    mkdir -p "$(dirname "$marker")"
+    touch "$marker"
+    cat >&2 <<'EOF'
+提示: 未找到 git-credential-libsecret，当前使用内存缓存（默认 1 周过期或登出后失效）。
+
+安装持久化凭据存储:
+  Debian/Ubuntu:  sudo apt install libsecret-1-0 git-credential-libsecret
+  Fedora/RHEL:    sudo dnf install git-credential-libsecret
+  Arch Linux:     sudo pacman -S libsecret git
+EOF
+}
+
+if command -v git-credential-libsecret >/dev/null 2>&1; then
+    exec git-credential-libsecret "$@"
+fi
+
+warn_missing_libsecret
+exec git-credential-cache --timeout=604800 "$@"