feat(Avalonia): V0.2 新构建跨平台前端界面MAAUnified，合并代码请求 (#16048)

* feat(MaaUnified): MaaUnified构建完成，作为submodule加入

* fix(MaaUnified): 修复自动构建时 submodule拉取错误问题

* feat(MaaUnified): MaaUnified submodule更换为组织仓库

* ci: do not fetch useless module

---------

Co-authored-by: MistEO <mistereo@hotmail.com>

.github/scripts/sync-optional-submodules.sh

@@ -0,0 +1,68 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+mode="init"
+depth=""
+declare -a paths=()
+
+while (($# > 0)); do
+    case "$1" in
+        --init)
+            mode="init"
+            shift
+            ;;
+        --remote)
+            mode="remote"
+            shift
+            ;;
+        --depth)
+            depth="$2"
+            shift 2
+            ;;
+        --)
+            shift
+            paths+=("$@")
+            break
+            ;;
+        *)
+            paths+=("$1")
+            shift
+            ;;
+    esac
+done
+
+if ((${#paths[@]} == 0)); then
+    echo "Usage: $0 [--init|--remote] [--depth N] path [path ...]" >&2
+    exit 64
+fi
+
+is_submodule_path() {
+    local path="$1"
+
+    git config -f .gitmodules --get-regexp '^submodule\..*\.path$' 2>/dev/null \
+        | awk '{ print $2 }' \
+        | grep -Fxq "$path"
+}
+
+for path in "${paths[@]}"; do
+    if ! is_submodule_path "$path"; then
+        echo "Skipping $path: not configured as a submodule in .gitmodules."
+        continue
+    fi
+
+    if [[ "$mode" == "remote" ]]; then
+        echo "Updating submodule: $path"
+        git submodule update --remote "$path"
+        continue
+    fi
+
+    if [[ -n "$depth" ]]; then
+        echo "Initializing submodule: $path (depth=$depth)"
+        git submodule update --init --depth "$depth" "$path"
+        continue
+    fi
+
+    echo "Initializing submodule: $path"
+    git submodule update --init "$path"
+done