chore: 移除 Windows arm64 构建与发布支持

Windows ARM64 使用场景极少，windows-11-arm runner 上 MSYS2
CLANGARM64 交叉编译不稳定，CGO 编译问题难以排查，维护成本
远超收益。移除 arm64 的 CI 矩阵条目、Makefile Windows 变量、
versionctl 资产白名单、README 文档和规范中的相关需求。
Linux 和 macOS arm64 不受影响。

Makefile

@@ -35,17 +35,15 @@ ifeq ($(TARGET_ARCH),arm64)
 APPIMAGE_ARCH := aarch64
 DEB_ARCH := arm64
 RPM_ARCH := aarch64
-WINDOWS_WINDRES_FORMAT_BFD := pe-aarch64
-WINDOWS_WINDRES_FORMAT_LLVM := aarch64-w64-mingw32
-WINDOWS_RESOURCE := rsrc_windows_arm64.syso
 else
 APPIMAGE_ARCH := x86_64
 DEB_ARCH := amd64
 RPM_ARCH := x86_64
+endif
+
 WINDOWS_WINDRES_FORMAT_BFD := pe-x86-64
 WINDOWS_WINDRES_FORMAT_LLVM := x86_64-w64-mingw32
 WINDOWS_RESOURCE := rsrc_windows_amd64.syso
-endif
 
 APPIMAGETOOL_PATH := build/tools/appimagetool-$(APPIMAGE_ARCH).AppImage
 APPIMAGETOOL_URL ?= https://github.com/AppImage/AppImageKit/releases/download/continuous/appimagetool-$(APPIMAGE_ARCH).AppImage
@@ -163,7 +161,7 @@ _desktop-test:
 	cd backend && go test ./cmd/desktop/... -v
 
 _desktop-clean:
-	rm -rf build/ embedfs/assets embedfs/frontend-dist backend/cmd/desktop/rsrc_windows_amd64.syso backend/cmd/desktop/rsrc_windows_arm64.syso
+	rm -rf build/ embedfs/assets embedfs/frontend-dist backend/cmd/desktop/rsrc_windows_amd64.syso
 
 _desktop-prepare-frontend: _frontend-install
 	@printf 'Preparing frontend for desktop...\n'
@@ -283,7 +281,7 @@ _check-linux-target-arch:
 	fi
 
 _check-windows-target-arch:
-	@if [ "$(TARGET_ARCH)" != "amd64" ] && [ "$(TARGET_ARCH)" != "arm64" ]; then \
+	@if [ "$(TARGET_ARCH)" != "amd64" ]; then \
 		printf 'Unsupported Windows TARGET_ARCH: %s\n' "$(TARGET_ARCH)"; \
 		exit 1; \
 	fi