Add monitored npm install with timeout and fallback registry.

Improve container startup by printing periodic install heartbeat logs, enforcing npm install timeout, and retrying with a fallback registry to avoid silent hangs.

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

README.md

@@ -83,6 +83,7 @@ DOCKER_BUILDKIT=1 docker build --network=host \
 docker run --rm -it \
   -p 14620:14620 \
   -p 14621:14621 \
+  -v media_crawler_runtime:/app/runtime \
   --env-file backend/.env \
   -e GIT_REPO_URL=https://git.rc707blog.top/rose_cat707/media_crawler.git \
   -e GIT_BRANCH=main \
@@ -95,4 +96,8 @@ docker run --rm -it \
 - `GIT_BRANCH`：拉取分支（默认 `main`）
 - `WORKTREE_DIR`：容器内代码目录（默认 `/app/runtime`）
 - `NPM_REGISTRY`：前端依赖安装镜像源（默认 `https://registry.npmmirror.com`）
+- `NPM_FALLBACK_REGISTRY`：`NPM_REGISTRY` 失败时回退源（默认 `https://registry.npmjs.org`）
+- `FORCE_FRONTEND_REBUILD`：强制每次重装前端依赖并重建（默认 `0`，仅 lockfile 变更时才安装构建）
+- `NPM_INSTALL_TIMEOUT_SEC`：前端依赖安装超时秒数（默认 `900`）
+- `NPM_PROGRESS_INTERVAL_SEC`：安装过程心跳日志间隔秒数（默认 `15`）