fix(setup): silence prompt on non-tty stdin and emit per-target launch hints

The Linux one-click-start and setup_backend_linux scripts were both
assuming interactive stdin:

- one-click-start.sh called `read -r -p ...` on every fatal exit path
  (non-Linux host, missing release files, install failure, missing
  weight). When the script is launched from a desktop entry, systemd
  user unit, CI, or any other context where stdin is not a TTY, `read`
  would block waiting for input that will never come, hanging the
  process instead of exiting promptly. Replace each site with a small
  `pause_if_tty` helper that only prompts when `[ -t 0 ]`, so the
  script still pauses for a user at a real terminal but returns
  immediately when run unattended.

- scripts/setup_backend_linux.sh printed a single, hard-coded launch
  block that only mentioned `.venv_paddle` (CPU). After the previous
  --target auto/cpu/gpu/both refactor, the user could have built any
  combination of CPU and GPU venvs but the hints always pointed at the
  CPU one. Wrap the post-install message in `print_completion_hints`,
  iterate over the actually-selected modes to print the correct
  `<venv>/bin/python` for each (CPU -> .venv_paddle, GPU ->
  .venv_paddle_gpu), and add an auto-mode command line when both
  venvs exist or a hint to install the CPU fallback when only GPU
  was built.

No behaviour change for the install flow itself; only the prompt
handling and the post-install guidance.

one-click-start.sh

@@ -85,11 +85,18 @@ EOF
 # ── 1. 检查系统和 Release 文件 ────────────────────────────────
 if [ "$(uname -s)" != "Linux" ]; then
     echo "[错误] 此脚本仅支持 Linux。" >&2
-    read -r -p "按回车键退出..."
+    pause_if_tty "按回车键退出..."
     exit 1
 fi
 
 # ── 辅助函数 ───────────────────────────────────────────────────
+pause_if_tty() {
+    local prompt="${1:-按回车键退出...}"
+    if [ -t 0 ]; then
+        read -r -p "$prompt"
+    fi
+}
+
 has_nvidia_gpu() {
     command -v nvidia-smi >/dev/null 2>&1 && nvidia-smi -L >/dev/null 2>&1
 }
@@ -152,7 +159,7 @@ assert_required_files() {
             echo "       - $item" >&2
         done
         echo "Please re-extract the full latest release zip and retry." >&2
-        read -r -p "Press Enter to exit"
+        pause_if_tty "Press Enter to exit"
         exit 1
     fi
 }
@@ -255,7 +262,7 @@ if [ "$READY" -eq 0 ]; then
             echo "       Auto mode already attempted GPU/CPU fallback." >&2
         fi
         echo "       完整安装日志已保存到 logs/backend-install.log，排查请提供此文件。" >&2
-        read -r -p "按回车键退出..."
+        pause_if_tty "按回车键退出..."
         exit 1
     fi
 fi
@@ -273,7 +280,7 @@ WEIGHT="$SCRIPT_DIR/models/weights/yolo-captcha-detector.pt"
 if [ ! -f "$WEIGHT" ]; then
     echo "[错误] 缺少检测权重：$WEIGHT" >&2
     echo "       请从 Release 包补齐 models/weights/yolo-captcha-detector.pt 后再启动。" >&2
-    read -r -p "按回车键退出..."
+    pause_if_tty "按回车键退出..."
     exit 1
 fi
 

scripts/setup_backend_linux.sh

@@ -272,15 +272,43 @@ else
 fi
 
 # ── 7. 完成 ────────────────────────────────────────────────────
-cat <<EOF
+print_completion_hints() {
+    local mode py has_cpu=0 has_gpu=0
 
-完成。启动后端：
+    for mode in "${SELECTED[@]}"; do
+        case "$mode" in
+            cpu) has_cpu=1 ;;
+            gpu) has_gpu=1 ;;
+        esac
+    done
 
-  GUI 模式：
-    $ROOT/.venv_paddle/bin/python $ROOT/scripts/tools/start_backend.py --mode auto
+    echo ""
+    echo "完成。启动后端："
+    echo ""
 
-  headless 模式：
-    $ROOT/.venv_paddle/bin/python $ROOT/scripts/tools/start_backend.py --headless --mode auto
+    for mode in "${SELECTED[@]}"; do
+        if [ "$mode" = "gpu" ]; then
+            py="$ROOT/.venv_paddle_gpu/bin/python"
+        else
+            py="$ROOT/.venv_paddle/bin/python"
+        fi
+        echo "  ${mode^^} 环境："
+        echo "    GUI:      $py $ROOT/scripts/tools/start_backend.py --mode $mode"
+        echo "    headless: $py $ROOT/scripts/tools/start_backend.py --headless --mode $mode"
+        echo ""
+    done
 
-  Linux 支持 CPU；如 NVIDIA/CUDA/PaddlePaddle 环境可用，也支持 GPU/auto 模式。
-EOF
+    if [ "$has_gpu" -eq 1 ] && [ "$has_cpu" -eq 1 ]; then
+        echo "  auto 模式（GPU 优先，失败回退 CPU）："
+        echo "    $ROOT/.venv_paddle_gpu/bin/python $ROOT/scripts/tools/start_backend.py --headless --mode auto"
+        echo ""
+    elif [ "$has_gpu" -eq 1 ]; then
+        echo "  提示：使用 auto 模式前，建议再安装 CPU 回退环境："
+        echo "    ./scripts/setup_backend_linux.sh --target cpu"
+        echo ""
+    fi
+
+    echo "  Linux 支持 CPU；如 NVIDIA/CUDA/PaddlePaddle 环境可用，也支持 GPU/auto 模式。"
+}
+
+print_completion_hints